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>

database/migrations/2026_08_06_203010_create_workflow_templates_table.php

@@ -0,0 +1,32 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('workflow_templates', function (Blueprint $table) {
+            $table->id();
+            $table->string('name');
+            $table->text('description')->nullable();
+            // Ordered array of step definitions, e.g.
+            // [{"type": "script_generation", "requires_approval": true}, ...]
+            $table->json('steps');
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('workflow_templates');
+    }
+};

database/migrations/2026_08_06_203011_create_video_projects_table.php

@@ -0,0 +1,36 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * Deliberately independent of the existing projects/tasks/ideas tables —
+     * no foreign keys into them. See Task #47 on the "YouTube Content
+     * Creation System" project for why.
+     */
+    public function up(): void
+    {
+        Schema::create('video_projects', function (Blueprint $table) {
+            $table->id();
+            $table->string('title');
+            $table->text('description')->nullable();
+            $table->string('status')->default('draft');
+            $table->foreignId('workflow_template_id')->nullable()->constrained()->nullOnDelete();
+            $table->softDeletes();
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('video_projects');
+    }
+};

database/migrations/2026_08_06_203012_create_workflow_steps_table.php

@@ -0,0 +1,39 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('workflow_steps', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('video_project_id')->constrained()->cascadeOnDelete();
+            $table->string('type');
+            $table->unsignedInteger('order');
+            $table->string('status')->default('pending');
+            $table->boolean('requires_approval')->default(false);
+            $table->json('input')->nullable();
+            $table->json('output')->nullable();
+            $table->text('error')->nullable();
+            $table->timestamp('started_at')->nullable();
+            $table->timestamp('completed_at')->nullable();
+            $table->timestamps();
+
+            $table->unique(['video_project_id', 'order']);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('workflow_steps');
+    }
+};

database/migrations/2026_08_06_203013_create_assets_table.php

@@ -0,0 +1,35 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('assets', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('video_project_id')->constrained()->cascadeOnDelete();
+            $table->foreignId('workflow_step_id')->nullable()->constrained()->nullOnDelete();
+            $table->string('type');
+            $table->string('disk_path');
+            $table->string('mime_type')->nullable();
+            $table->unsignedBigInteger('size_bytes')->nullable();
+            $table->unsignedInteger('version')->default(1);
+            $table->json('metadata')->nullable();
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('assets');
+    }
+};

database/migrations/2026_08_06_203014_create_ai_providers_table.php

@@ -0,0 +1,32 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('ai_providers', function (Blueprint $table) {
+            $table->id();
+            $table->string('name');
+            $table->string('provider');
+            $table->string('api_key');
+            $table->json('config')->nullable();
+            $table->boolean('is_active')->default(true);
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('ai_providers');
+    }
+};