feat: add community activity feed and mentions

app/Http/Controllers/Api/CommunityActivityController.php

@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Controllers\Api;
+
+use App\Http\Controllers\Controller;
+use App\Services\CommunityActivityService;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+
+final class CommunityActivityController extends Controller
+{
+    public function __construct(private readonly CommunityActivityService $activityService)
+    {
+    }
+
+    public function index(Request $request): JsonResponse
+    {
+        $filter = $this->resolveFilter($request);
+
+        if ($this->activityService->requiresAuthentication($filter) && ! $request->user()) {
+            return response()->json(['error' => 'Unauthenticated'], 401);
+        }
+
+        $feed = $this->activityService->getFeed(
+            viewer: $request->user(),
+            filter: $filter,
+            page: (int) $request->query('page', 1),
+            perPage: (int) $request->query('per_page', CommunityActivityService::DEFAULT_PER_PAGE),
+            actorUserId: $request->filled('user_id') ? (int) $request->query('user_id') : null,
+        );
+
+        return response()->json($feed);
+    }
+
+    private function resolveFilter(Request $request): string
+    {
+        if ($request->boolean('following') && ! $request->filled('filter')) {
+            return 'following';
+        }
+
+        return (string) $request->query('filter', 'all');
+    }
+}