Migrate user/profile URLs to /u/[handle] and remove legacy scripts

All user and post profile URLs have been updated from /[handle] to /u/[handle] for consistency. Added a redirect page for /posts/[id] to the canonical /u/[handle]/posts/[id] route. Deprecated and removed legacy scripts and documentation related to chat and federation endpoints. Push-based federation endpoints are now disabled in favor of real-time pull-based federation.

src/app/api/notifications/route.ts

@@ -102,6 +102,7 @@ export async function GET(request: Request) {
                 post: row.postId ? {
                     id: row.postId,
                     content: row.postContent,
+                    authorHandle: row.actorHandle, // The actor is the post author for likes/reposts
                 } : null,
             };
         });