feat: forum rich-text editor, emoji picker, mentions, discover nav, feed, uploads, profile

Forum:
- TipTap WYSIWYG editor with full toolbar
- @emoji-mart/react emoji picker (consistent with tweets)
- @mention autocomplete with user search API
- Fix PHP 8.4 parse errors in Blade templates
- Fix thread data display (paginator items)
- Align forum page widths to max-w-5xl

Discover:
- Extract shared _nav.blade.php partial
- Add missing nav links to for-you page
- Add Following link for authenticated users

Feed/Posts:
- Post model, controllers, policies, migrations
- Feed page components (PostComposer, FeedCard, etc)
- Post reactions, comments, saves, reports, sharing
- Scheduled publishing support
- Link preview controller

Profile:
- Profile page components (ProfileHero, ProfileTabs)
- Profile API controller

Uploads:
- Upload wizard enhancements
- Scheduled publish picker
- Studio status bar and readiness checklist

app/Http/Requests/Posts/CreateCommentRequest.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace App\Http\Requests\Posts;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class CreateCommentRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return (bool) $this->user();
+    }
+
+    public function rules(): array
+    {
+        return [
+            'body' => ['required', 'string', 'min:1', 'max:1000'],
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'body.max' => 'Comment cannot exceed 1,000 characters.',
+        ];
+    }
+}

app/Http/Requests/Posts/CreatePostRequest.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace App\Http\Requests\Posts;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class CreatePostRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return (bool) $this->user();
+    }
+
+    public function rules(): array
+    {
+        return [
+            'type'                      => ['required', 'string', 'in:text,artwork_share,upload,achievement'],
+            'visibility'                => ['required', 'string', 'in:public,followers,private'],
+            'body'                      => ['nullable', 'string', 'max:2000'],
+            'targets'                   => ['nullable', 'array', 'max:1'],
+            'targets.*.type'            => ['required_with:targets', 'string', 'in:artwork'],
+            'targets.*.id'              => ['required_with:targets', 'integer', 'min:1'],
+            'link_preview'              => ['nullable', 'array'],
+            'link_preview.url'          => ['nullable', 'string', 'url', 'max:2048'],
+            'link_preview.title'        => ['nullable', 'string', 'max:300'],
+            'link_preview.description'  => ['nullable', 'string', 'max:500'],
+            'link_preview.image'        => ['nullable', 'string', 'url', 'max:2048'],
+            'link_preview.site_name'    => ['nullable', 'string', 'max:100'],
+            'tagged_users'              => ['nullable', 'array', 'max:10'],
+            'tagged_users.*.id'         => ['required_with:tagged_users', 'integer', 'min:1'],
+            'tagged_users.*.username'   => ['required_with:tagged_users', 'string', 'max:50'],
+            'tagged_users.*.name'       => ['nullable', 'string', 'max:100'],
+            'publish_at'                => ['nullable', 'date', 'after:now'],
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'body.max' => 'Post body cannot exceed 2,000 characters.',
+        ];
+    }
+}

app/Http/Requests/Posts/ShareArtworkRequest.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Http\Requests\Posts;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class ShareArtworkRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return (bool) $this->user();
+    }
+
+    public function rules(): array
+    {
+        return [
+            'body'       => ['nullable', 'string', 'max:2000'],
+            'visibility' => ['required', 'string', 'in:public,followers,private'],
+        ];
+    }
+}

app/Http/Requests/Posts/UpdatePostRequest.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Http\Requests\Posts;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class UpdatePostRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return (bool) $this->user();
+    }
+
+    public function rules(): array
+    {
+        return [
+            'body'       => ['nullable', 'string', 'max:2000'],
+            'visibility' => ['nullable', 'string', 'in:public,followers,private'],
+        ];
+    }
+}