Add AI provider abstraction and asset storage (tasks #33, #34)

AiProviderDriver: one generic interface (generate(prompt, options) ->
AiGenerationResult) rather than per-capability interfaces, since text
(OpenAI chat completions), image (StabilityAI stable-image), and
speech (ElevenLabs TTS) generation all reduce to prompt-in/content-out.
Drivers throw AiGenerationException on failure; AiProviderManager
resolves the right driver from an AiProvider record's `provider`
column and guards on is_active. Real request/response shapes per each
provider's API, verified with Http::fake() — no live API keys
available yet to smoke test against the real services.

AssetStorage: stores generated content under
video-projects/{id}/{type}/v{n}.{ext}, versioned per (project, type[,
step]) slot so retries don't clobber earlier output, plus
contents/url/delete and pruneOldVersions for cleanup.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/Feature/AiProviders/AiProviderManagerTest.php

@@ -0,0 +1,46 @@
+<?php
+
+use App\Models\AiProvider;
+use App\Support\AiProviders\AiGenerationException;
+use App\Support\AiProviders\AiGenerationResult;
+use App\Support\AiProviders\AiProviderDriver;
+use App\Support\AiProviders\AiProviderManager;
+
+test('it dispatches to the driver registered for the provider key', function () {
+    $driver = new class implements AiProviderDriver
+    {
+        public function generate(AiProvider $provider, string $prompt, array $options = []): AiGenerationResult
+        {
+            return new AiGenerationResult("echo: {$prompt}", 'text/plain');
+        }
+    };
+
+    $manager = new AiProviderManager(['openai' => $driver]);
+    $provider = AiProvider::factory()->create(['provider' => 'openai']);
+
+    $result = $manager->generate($provider, 'hello');
+
+    expect($result->content)->toBe('echo: hello');
+});
+
+test('it throws when no driver is registered for the provider key', function () {
+    $manager = new AiProviderManager([]);
+    $provider = AiProvider::factory()->create(['provider' => 'openai']);
+
+    $manager->generate($provider, 'hello');
+})->throws(AiGenerationException::class, "No driver registered for AI provider 'openai'");
+
+test('it refuses to generate with an inactive provider', function () {
+    $driver = new class implements AiProviderDriver
+    {
+        public function generate(AiProvider $provider, string $prompt, array $options = []): AiGenerationResult
+        {
+            throw new RuntimeException('should not be called');
+        }
+    };
+
+    $manager = new AiProviderManager(['openai' => $driver]);
+    $provider = AiProvider::factory()->create(['provider' => 'openai', 'is_active' => false]);
+
+    $manager->generate($provider, 'hello');
+})->throws(AiGenerationException::class, 'is not active');

tests/Feature/AiProviders/ElevenLabsDriverTest.php

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+<?php
+
+use App\Models\AiProvider;
+use App\Support\AiProviders\AiGenerationException;
+use App\Support\AiProviders\ElevenLabsDriver;
+use Illuminate\Support\Facades\Http;
+
+test('it generates audio successfully', function () {
+    Http::fake([
+        'api.elevenlabs.io/*' => Http::response('fake-mp3-bytes', 200, ['Content-Type' => 'audio/mpeg']),
+    ]);
+
+    $provider = AiProvider::factory()->create([
+        'provider' => 'elevenlabs',
+        'api_key' => 'el-test',
+        'config' => ['voice_id' => 'voice123'],
+    ]);
+
+    $result = (new ElevenLabsDriver)->generate($provider, 'Hello world');
+
+    expect($result->content)->toBe('fake-mp3-bytes');
+    expect($result->contentType)->toBe('audio/mpeg');
+
+    Http::assertSent(function ($request) {
+        return $request->url() === 'https://api.elevenlabs.io/v1/text-to-speech/voice123'
+            && $request->hasHeader('xi-api-key', 'el-test')
+            && $request['text'] === 'Hello world';
+    });
+});
+
+test('a voice_id passed in options overrides the provider config', function () {
+    Http::fake(['api.elevenlabs.io/*' => Http::response('bytes')]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'elevenlabs', 'config' => ['voice_id' => 'default-voice']]);
+
+    (new ElevenLabsDriver)->generate($provider, 'hi', ['voice_id' => 'custom-voice']);
+
+    Http::assertSent(fn ($request) => str_contains($request->url(), '/text-to-speech/custom-voice'));
+});
+
+test('it throws when no voice_id is configured anywhere', function () {
+    $provider = AiProvider::factory()->create(['provider' => 'elevenlabs', 'config' => null]);
+
+    (new ElevenLabsDriver)->generate($provider, 'hi');
+})->throws(AiGenerationException::class, 'no voice_id configured');
+
+test('it throws when ElevenLabs returns an error', function () {
+    Http::fake([
+        'api.elevenlabs.io/*' => Http::response(['detail' => ['message' => 'quota exceeded']], 429),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'elevenlabs', 'config' => ['voice_id' => 'v1']]);
+
+    (new ElevenLabsDriver)->generate($provider, 'hi');
+})->throws(AiGenerationException::class, 'quota exceeded');

tests/Feature/AiProviders/OpenAiDriverTest.php

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+<?php
+
+use App\Models\AiProvider;
+use App\Support\AiProviders\AiGenerationException;
+use App\Support\AiProviders\OpenAiDriver;
+use Illuminate\Support\Facades\Http;
+
+test('it generates text successfully', function () {
+    Http::fake([
+        'api.openai.com/*' => Http::response([
+            'choices' => [
+                ['message' => ['content' => 'Once upon a time...']],
+            ],
+        ], 200),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'openai', 'api_key' => 'sk-test']);
+
+    $result = (new OpenAiDriver)->generate($provider, 'Write a story opener');
+
+    expect($result->content)->toBe('Once upon a time...');
+    expect($result->contentType)->toBe('text/plain');
+
+    Http::assertSent(function ($request) {
+        return $request->url() === 'https://api.openai.com/v1/chat/completions'
+            && $request->hasHeader('Authorization', 'Bearer sk-test')
+            && $request['messages'][0]['content'] === 'Write a story opener'
+            && $request['model'] === 'gpt-4o-mini';
+    });
+});
+
+test('it uses a model from options over the provider config over the default', function () {
+    Http::fake([
+        'api.openai.com/*' => Http::response(['choices' => [['message' => ['content' => 'hi']]]]),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'openai', 'config' => ['model' => 'gpt-4o']]);
+
+    (new OpenAiDriver)->generate($provider, 'hi', ['model' => 'gpt-4-turbo']);
+
+    Http::assertSent(fn ($request) => $request['model'] === 'gpt-4-turbo');
+});
+
+test('it throws when OpenAI returns an error', function () {
+    Http::fake([
+        'api.openai.com/*' => Http::response(['error' => ['message' => 'Invalid API key']], 401),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'openai']);
+
+    (new OpenAiDriver)->generate($provider, 'hi');
+})->throws(AiGenerationException::class, 'Invalid API key');
+
+test('it throws when the response has no message content', function () {
+    Http::fake([
+        'api.openai.com/*' => Http::response(['choices' => []]),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'openai']);
+
+    (new OpenAiDriver)->generate($provider, 'hi');
+})->throws(AiGenerationException::class);

tests/Feature/AiProviders/StabilityAiDriverTest.php

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+<?php
+
+use App\Models\AiProvider;
+use App\Support\AiProviders\AiGenerationException;
+use App\Support\AiProviders\StabilityAiDriver;
+use Illuminate\Support\Facades\Http;
+
+test('it generates an image successfully', function () {
+    $bytes = 'fake-png-bytes';
+
+    Http::fake([
+        'api.stability.ai/*' => Http::response([
+            'image' => base64_encode($bytes),
+            'seed' => 42,
+            'finish_reason' => 'SUCCESS',
+        ], 200),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'stability_ai', 'api_key' => 'sk-test']);
+
+    $result = (new StabilityAiDriver)->generate($provider, 'a red bicycle');
+
+    expect($result->content)->toBe($bytes);
+    expect($result->contentType)->toBe('image/png');
+    expect($result->raw['seed'])->toBe(42);
+
+    Http::assertSent(function ($request) {
+        return $request->url() === 'https://api.stability.ai/v2beta/stable-image/generate/core'
+            && $request->hasHeader('Authorization', 'Bearer sk-test');
+    });
+});
+
+test('it respects an output_format override', function () {
+    Http::fake([
+        'api.stability.ai/*' => Http::response(['image' => base64_encode('bytes')]),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'stability_ai']);
+
+    $result = (new StabilityAiDriver)->generate($provider, 'prompt', ['output_format' => 'webp']);
+
+    expect($result->contentType)->toBe('image/webp');
+});
+
+test('it throws when StabilityAI returns an error', function () {
+    Http::fake([
+        'api.stability.ai/*' => Http::response(['errors' => ['invalid prompt']], 400),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'stability_ai']);
+
+    (new StabilityAiDriver)->generate($provider, 'prompt');
+})->throws(AiGenerationException::class, 'invalid prompt');
+
+test('it throws when the response has no image data', function () {
+    Http::fake([
+        'api.stability.ai/*' => Http::response(['finish_reason' => 'CONTENT_FILTERED']),
+    ]);
+
+    $provider = AiProvider::factory()->create(['provider' => 'stability_ai']);
+
+    (new StabilityAiDriver)->generate($provider, 'prompt');
+})->throws(AiGenerationException::class);