feat(user): add GET /api/me endpoint for authenticated user profile
Add a new /api/me endpoint that returns the authenticated user's own
profile with stats. This provides a convenient way for the frontend to
fetch the current user's profile without needing to know their DID.
Changes:
- Add MeHandler with HandleMe serving GET /api/me
- Register route with RequireAuth middleware
- Generalize handleServiceError with operation parameter for reuse
- Add 6 unit tests covering success, nil stats, auth, errors, timeout
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>