Add Video Projects schema and workflow engine core (tasks #31, #32)

Foundational layer for the YouTube Content Creation System project,
built as a fully independent domain per the earlier decision (task
#47) — no foreign keys into the existing projects/tasks/ideas tables.

Schema: video_projects, workflow_steps, assets, ai_providers,
workflow_templates (named to avoid colliding with the existing
Post-templates `templates` table).

WorkflowEngine (app/Support/VideoWorkflow/) drives a project's step
sequence: start/startFromTemplate, currentStep, completeStep (with
optional approval gating), approveStep/rejectStep, failStep/retryStep,
skipStep. It only manages state transitions — actual step execution
(AI calls, rendering, etc.) is out of scope here (tasks #33+).

Also fixes four Publisher classes (WordPress/Reddit/Twitter/LinkedIn)
that were missing a `use App\Models\SocialAccount;` import after an
earlier interface change, which broke the entire test suite at
bootstrap; and PostFactory, which still set the now-removed
`social_account_id` column instead of the SocialAccount pivot.

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

tests/Feature/VideoWorkflow/VideoWorkflowModelsTest.php

@@ -0,0 +1,98 @@
+<?php
+
+use App\Models\AiProvider;
+use App\Models\Asset;
+use App\Models\VideoProject;
+use App\Models\WorkflowStep;
+use App\Models\WorkflowTemplate;
+
+test('a video project has ordered steps', function () {
+    $project = VideoProject::factory()->create();
+    WorkflowStep::factory()->for($project)->create(['type' => 'video_generation', 'order' => 1]);
+    WorkflowStep::factory()->for($project)->create(['type' => 'script_generation', 'order' => 0]);
+
+    expect($project->steps->pluck('type')->all())->toBe(['script_generation', 'video_generation']);
+});
+
+test('a video project belongs to a workflow template', function () {
+    $template = WorkflowTemplate::factory()->create();
+    $project = VideoProject::factory()->create(['workflow_template_id' => $template->id]);
+
+    expect($project->workflowTemplate->id)->toBe($template->id);
+    expect($template->videoProjects->first()->id)->toBe($project->id);
+});
+
+test('deleting a video project cascades to its steps and assets', function () {
+    $project = VideoProject::factory()->create();
+    $step = WorkflowStep::factory()->for($project)->create();
+    $asset = Asset::factory()->for($project)->create(['workflow_step_id' => $step->id]);
+
+    $project->forceDelete();
+
+    expect(WorkflowStep::find($step->id))->toBeNull();
+    expect(Asset::find($asset->id))->toBeNull();
+});
+
+test('a video project is soft deleted by default', function () {
+    $project = VideoProject::factory()->create();
+
+    $project->delete();
+
+    expect(VideoProject::find($project->id))->toBeNull();
+    expect(VideoProject::withTrashed()->find($project->id))->not->toBeNull();
+});
+
+test('deleting the workflow step an asset belongs to nulls the reference instead of deleting the asset', function () {
+    $project = VideoProject::factory()->create();
+    $step = WorkflowStep::factory()->for($project)->create();
+    $asset = Asset::factory()->for($project)->create(['workflow_step_id' => $step->id]);
+
+    $step->delete();
+
+    expect($asset->fresh()->workflow_step_id)->toBeNull();
+});
+
+test('workflow step input/output/requires_approval cast correctly', function () {
+    $step = WorkflowStep::factory()->create([
+        'requires_approval' => true,
+        'input' => ['prompt' => 'write a script'],
+        'output' => ['script' => 'once upon a time'],
+    ]);
+
+    expect($step->fresh())
+        ->requires_approval->toBeTrue()
+        ->input->toBe(['prompt' => 'write a script'])
+        ->output->toBe(['script' => 'once upon a time']);
+});
+
+test('asset metadata casts to an array', function () {
+    $asset = Asset::factory()->create(['metadata' => ['duration_seconds' => 42]]);
+
+    expect($asset->fresh()->metadata)->toBe(['duration_seconds' => 42]);
+});
+
+test('an ai provider stores its config as an array and defaults to active', function () {
+    $provider = AiProvider::factory()->create([
+        'provider' => 'elevenlabs',
+        'config' => ['voice_id' => 'abc123'],
+    ]);
+
+    expect($provider->fresh())
+        ->provider->toBe('elevenlabs')
+        ->config->toBe(['voice_id' => 'abc123'])
+        ->is_active->toBeTrue();
+});
+
+test('a workflow template stores its steps as an ordered array', function () {
+    $template = WorkflowTemplate::factory()->create([
+        'steps' => [
+            ['type' => 'script_generation', 'requires_approval' => true],
+            ['type' => 'youtube_publish', 'requires_approval' => false],
+        ],
+    ]);
+
+    expect($template->fresh()->steps)->toBe([
+        ['type' => 'script_generation', 'requires_approval' => true],
+        ['type' => 'youtube_publish', 'requires_approval' => false],
+    ]);
+});