feat: add Post model, migration, and factory

Adds the Post model belonging to Site (required, cascade-deletes with
the site) and SocialAccount (nullable, nulled out on account delete).
Foundation for the Scheduled Posts feature; later tasks build the
Livewire CRUD UI and API on top of this model.

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

app/Models/Post.php

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+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class Post extends Model
+{
+    use HasFactory;
+
+    public const TYPES = [
+        'twitter', 'instagram', 'facebook', 'reddit',
+        'tiktok', 'linkedin', 'youtube', 'blog', 'other',
+    ];
+
+    public const STATUSES = ['draft', 'scheduled', 'published', 'failed'];
+
+    protected $fillable = [
+        'site_id',
+        'social_account_id',
+        'type',
+        'title',
+        'body',
+        'status',
+        'scheduled_at',
+    ];
+
+    protected $casts = [
+        'scheduled_at' => 'datetime',
+    ];
+
+    public function site(): BelongsTo
+    {
+        return $this->belongsTo(Site::class);
+    }
+
+    public function socialAccount(): BelongsTo
+    {
+        return $this->belongsTo(SocialAccount::class);
+    }
+}

database/factories/PostFactory.php

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+<?php
+
+namespace Database\Factories;
+
+use App\Models\Post;
+use App\Models\Site;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class PostFactory extends Factory
+{
+    protected $model = Post::class;
+
+    public function definition(): array
+    {
+        return [
+            'site_id' => Site::factory(),
+            'social_account_id' => null,
+            'type' => fake()->randomElement(Post::TYPES),
+            'title' => fake()->optional()->sentence(),
+            'body' => fake()->paragraph(),
+            'status' => fake()->randomElement(Post::STATUSES),
+            'scheduled_at' => fake()->optional()->dateTimeBetween('now', '+1 month'),
+        ];
+    }
+}

database/migrations/2026_07_18_135721_create_posts_table.php

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+<?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('posts', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('site_id')->constrained()->cascadeOnDelete();
+            $table->foreignId('social_account_id')->nullable()->constrained()->nullOnDelete();
+            $table->enum('type', [
+                'twitter', 'instagram', 'facebook', 'reddit',
+                'tiktok', 'linkedin', 'youtube', 'blog', 'other',
+            ]);
+            $table->string('title')->nullable();
+            $table->text('body');
+            $table->enum('status', ['draft', 'scheduled', 'published', 'failed'])->default('draft');
+            $table->timestamp('scheduled_at')->nullable();
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('posts');
+    }
+};

tests/Feature/PostModelTest.php

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+<?php
+
+use App\Models\Post;
+use App\Models\Site;
+use App\Models\SocialAccount;
+
+test('a post can be created with required fields only', function () {
+    $site = Site::factory()->create();
+
+    $post = Post::create([
+        'site_id' => $site->id,
+        'type' => 'blog',
+        'body' => 'Hello world',
+    ]);
+
+    $fresh = $post->fresh();
+
+    expect($fresh)
+        ->site_id->toBe($site->id)
+        ->type->toBe('blog')
+        ->body->toBe('Hello world')
+        ->status->toBe('draft')
+        ->social_account_id->toBeNull()
+        ->title->toBeNull()
+        ->scheduled_at->toBeNull();
+});
+
+test('a post can be created with an account, title, status, and schedule', function () {
+    $site = Site::factory()->create();
+    $account = SocialAccount::factory()->create();
+
+    $post = Post::create([
+        'site_id' => $site->id,
+        'social_account_id' => $account->id,
+        'type' => 'twitter',
+        'title' => 'Launch day',
+        'body' => 'We just launched!',
+        'status' => 'scheduled',
+        'scheduled_at' => '2026-08-01 09:00:00',
+    ]);
+
+    $fresh = $post->fresh();
+
+    expect($fresh)
+        ->social_account_id->toBe($account->id)
+        ->title->toBe('Launch day')
+        ->status->toBe('scheduled')
+        ->scheduled_at->not->toBeNull();
+});
+
+test('a post belongs to a site', function () {
+    $site = Site::factory()->create();
+    $post = Post::factory()->create(['site_id' => $site->id]);
+
+    expect($post->site)->toBeInstanceOf(Site::class);
+    expect($post->site->id)->toBe($site->id);
+});
+
+test('a post can belong to a social account', function () {
+    $account = SocialAccount::factory()->create();
+    $post = Post::factory()->create(['social_account_id' => $account->id]);
+
+    expect($post->socialAccount)->toBeInstanceOf(SocialAccount::class);
+    expect($post->socialAccount->id)->toBe($account->id);
+});
+
+test('deleting a site cascades and deletes its posts', function () {
+    $site = Site::factory()->create();
+    $post = Post::factory()->create(['site_id' => $site->id]);
+
+    $site->delete();
+
+    expect(Post::find($post->id))->toBeNull();
+});
+
+test('deleting a social account nulls out the post link but keeps the post', function () {
+    $account = SocialAccount::factory()->create();
+    $post = Post::factory()->create(['social_account_id' => $account->id]);
+
+    $account->delete();
+
+    expect($post->fresh())
+        ->not->toBeNull()
+        ->social_account_id->toBeNull();
+});