Full end-to-end implementation with DB, API, frontend, and realtime sync:

- Block/Mute: player_blocks table, block checks in chat/matchmaking/invites,
  blocked-list UI in settings, block/mute buttons in opponent menu
- View Other Player's Profile: friendship_status, block_status, action buttons
  (add friend/challenge/message/block), spectate live indicator
- Groups: create/join/leave, group chat with realtime, game invites with
  accept flow, member management (add/remove), notifications
- Spectate: find-active-match API, chess spectate scene with live board
  updates, tournament spectate buttons, profile "watching live" indicator

DB migrations: groups + group_members tables, chat_messages columns added.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>