feat: initial release of relaticle/comments

Filament comments package with:
- Polymorphic commenting on any Eloquent model
- Threaded replies with configurable depth
- @mentions with autocomplete and user search
- Emoji reactions with toggle and who-reacted tooltips
- File attachments via Livewire uploads
- Reply and mention notifications via Filament notification system
- Thread subscriptions for notification control
- Real-time broadcasting (opt-in Echo) with polling fallback
- Dark mode support
- CommentsAction, CommentsTableAction, CommentsEntry for Filament integration
- 204 tests, 421 assertions

database/migrations/create_comment_attachments_table.php.stub

@@ -0,0 +1,24 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('comment_attachments', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('comment_id')
+                ->constrained(config('comments.tables.comments', 'comments'))
+                ->cascadeOnDelete();
+            $table->string('file_path');
+            $table->string('original_name');
+            $table->string('mime_type');
+            $table->unsignedBigInteger('size');
+            $table->string('disk');
+            $table->timestamps();
+        });
+    }
+};