Migrate user profiles from /u/[handle] to /profile/[handle=handle] with a validated SvelteKit param matcher that accepts handles and DIDs while rejecting reserved route segments. The old /u/[handle] route now 301-redirects, and the legacy /profile/user route is removed entirely. Changes: - Add handle param matcher validating handles/DIDs against reserved segments - Move profile page + UserActions from /u/[handle] to /profile/[handle=handle] - Add 301 redirect from /u/[handle] to /profile/[handle] for backwards compat - Redirect /profile to /profile/{handle} for authenticated users, /login for guests - Move profile tabs and auth guard into (local_user) layout group - Update all navigation links (sidebar, navbar, command palette) to use new paths - Fix API NSIDs: getCommunityFeed and getProfile to match backend - Rewrite markdown link generation (photonify, linkify) from /u/ to /profile/ - Add tests for handle matcher, profile redirect, /u/ redirect, and photonify Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>