feat(social): per-game friend request to disguised robots + lobby/stats/tile cosmetics

Functional: the in-game add-friend handshake aimed at an auto-match opponent who is
secretly a pooled robot now records the request per (game, seat) in a new
robot_friend_requests table -- never against the shared robot account -- mirroring the
robot_blocks pattern. The shared account stays out of friendships, the "requested" state
is pinned to the seat (not leaked across the player's other games), the robot ignores it,
and a background reaper drops the row 7 days after its game finishes. The outgoing-requests
list carries these per-game rows so the seat control stays disabled across reloads. No
withdraw UI, per owner decision.

Cosmetics:
- Lobby: an in-progress game tints the viewer's own score number green when leading or
  tied, red when trailing (reusing --ok/--danger); scores now render in seat-number order,
  matching the over-the-board scoreboard.
- Stats: the per-variant best move is laid out on two lines -- the variant label, then the
  score (right-aligned in its column) and the word tiles (left-aligned) below it.
- Dark theme: the played-tile background is a touch darker so a player-placed tile reads
  with more contrast (light theme unchanged).

Docs (ARCHITECTURE, FUNCTIONAL + _ru mirror, backend README, UI_DESIGN) updated in the
same change.

pkg/fbs/scrabble.fbs

@@ -532,11 +532,24 @@ table IncomingRequestList {
   requests:[AccountRef];
 }
 
+// RobotFriendRef is one per-game friend request to a disguised-robot opponent: a
+// per-game record (not a real account) carrying the game name the player saw and the
+// game/seat it was sent in, so the in-game card can re-mark that seat as already
+// requested. Its id is the robot_friend_requests row.
+table RobotFriendRef {
+  id:string;
+  display_name:string;
+  game_id:string;
+  seat:int;
+}
+
 // OutgoingRequestList is the accounts the caller has already requested and cannot
 // (re-)request: a live pending request or one the addressee declined. The game's
-// "add to friends" item reads it to stay disabled across reloads.
+// "add to friends" item reads it to stay disabled across reloads. robots are the
+// per-game disguised-robot requests (not real accounts), added trailing.
 table OutgoingRequestList {
   requests:[AccountRef];
+  robots:[RobotFriendRef];
 }
 
 // FriendCode is a freshly issued one-time add-a-friend code (returned once).