feat: add community activity feed and mentions

database/migrations/2026_03_16_180000_create_user_mentions_table.php

@@ -0,0 +1,34 @@
+<?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('user_mentions', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('user_id');
+            $table->unsignedBigInteger('mentioned_user_id');
+            $table->unsignedBigInteger('artwork_id')->nullable();
+            $table->unsignedBigInteger('comment_id');
+            $table->timestamp('created_at')->useCurrent();
+
+            $table->unique(['comment_id', 'mentioned_user_id'], 'user_mentions_comment_user_unique');
+            $table->index(['mentioned_user_id', 'created_at'], 'user_mentions_mentioned_created_idx');
+            $table->index(['user_id', 'created_at'], 'user_mentions_actor_created_idx');
+
+            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
+            $table->foreign('mentioned_user_id')->references('id')->on('users')->onDelete('cascade');
+            $table->foreign('artwork_id')->references('id')->on('artworks')->onDelete('cascade');
+            $table->foreign('comment_id')->references('id')->on('artwork_comments')->onDelete('cascade');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('user_mentions');
+    }
+};