Add script/TTS step handlers, dashboard, and pipeline UI (#35, #36, #43, #44)

StepHandler abstraction (app/Support/VideoWorkflow/StepHandlers/) plugs
into WorkflowEngine without coupling it to how any given step type is
actually executed:
- ScriptGenerationHandler: builds a prompt from the project's title/
  description (or an explicit outline/tone/keywords/target length in
  step input), generates via an active OpenAI AiProvider, stores the
  result as a 'script' asset.
- TtsVoiceoverHandler: voices step.input.text, or falls back to the
  project's latest script asset, via an active ElevenLabs AiProvider;
  voice_id/model_id are configurable per step. No direct "speed"
  control — ElevenLabs' base TTS endpoint doesn't expose one.

RunWorkflowStepJob resolves a step's handler by type and runs it on
the queue, matching the existing PublishPostJob pattern (including a
stale-dispatch guard: no-op if the step isn't 'in_progress' anymore).

UI, under its own /video-projects routes and nav entry — separate
from /projects per the earlier decision:
- VideoProjects/Index (#43): list projects with status and step
  progress, create new ones.
- VideoProjects/Show (#44): start a project from a WorkflowTemplate or
  a hardcoded default 8-step pipeline; per-step Run/Approve/Reject/
  Retry/Skip actions; auto-queues the next step after any transition
  when a handler exists for its type (steps with no handler yet just
  sit in_progress rather than auto-failing); lists project assets.

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

tests/Feature/Jobs/RunWorkflowStepJobTest.php

@@ -0,0 +1,77 @@
+<?php
+
+use App\Jobs\RunWorkflowStepJob;
+use App\Models\AiProvider;
+use App\Models\VideoProject;
+use App\Support\AiProviders\AiProviderManager;
+use App\Support\VideoWorkflow\StepHandlers\StepHandlerManager;
+use App\Support\VideoWorkflow\WorkflowEngine;
+use Illuminate\Support\Facades\Http;
+use Illuminate\Support\Facades\Storage;
+
+beforeEach(function () {
+    Storage::fake();
+    $this->engine = new WorkflowEngine;
+});
+
+test('it runs the matching handler and completes the step', function () {
+    Http::fake(['api.openai.com/*' => Http::response(['choices' => [['message' => ['content' => 'a script']]]])]);
+    AiProvider::factory()->create(['provider' => 'openai']);
+
+    $project = VideoProject::factory()->create();
+    $step = $this->engine->start($project, [['type' => 'script_generation']]);
+
+    (new RunWorkflowStepJob($step->id))->handle(app(StepHandlerManager::class), $this->engine);
+
+    expect($step->fresh()->status)->toBe('completed');
+});
+
+test('it fails the step when no handler is registered for its type', function () {
+    $project = VideoProject::factory()->create();
+    $step = $this->engine->start($project, [['type' => 'video_generation']]);
+
+    (new RunWorkflowStepJob($step->id))->handle(app(StepHandlerManager::class), $this->engine);
+
+    expect($step->fresh())
+        ->status->toBe('failed')
+        ->error->toContain('No handler registered');
+});
+
+test('it does nothing for a step that is no longer in_progress', function () {
+    $project = VideoProject::factory()->create();
+    $step = $this->engine->start($project, [['type' => 'script_generation']]);
+    $this->engine->skipStep($step);
+
+    (new RunWorkflowStepJob($step->id))->handle(app(StepHandlerManager::class), $this->engine);
+
+    expect($step->fresh()->status)->toBe('skipped');
+});
+
+test('it does nothing for a missing step', function () {
+    (new RunWorkflowStepJob(999999))->handle(app(StepHandlerManager::class), $this->engine);
+})->throwsNoExceptions();
+
+test('it fails the step when the handler throws unexpectedly', function () {
+    $badHandler = new class implements \App\Support\VideoWorkflow\StepHandlers\StepHandler
+    {
+        public function type(): string
+        {
+            return 'script_generation';
+        }
+
+        public function handle(\App\Models\WorkflowStep $step, WorkflowEngine $engine): void
+        {
+            throw new \RuntimeException('boom');
+        }
+    };
+    $manager = new StepHandlerManager([$badHandler]);
+
+    $project = VideoProject::factory()->create();
+    $step = $this->engine->start($project, [['type' => 'script_generation']]);
+
+    (new RunWorkflowStepJob($step->id))->handle($manager, $this->engine);
+
+    expect($step->fresh())
+        ->status->toBe('failed')
+        ->error->toBe('boom');
+});