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.

docs/ARCHITECTURE.md

@@ -519,7 +519,13 @@ in either direction (the enqueue excludes the caller's `BlockedWith` set);
   expires after **30 days** and may be re-sent), or **decline** — a decline is
   remembered (`status='declined'`) and blocks further requests from that sender,
   unless they hand them a code, which overrides it. The requester's own cancel still
-  deletes the row. (Discovery by friend list or platform deep-link is future work.)
+  deletes the row. A request sent in-game to an **auto-match opponent who is secretly a
+  pooled robot** is recorded instead in a separate **`robot_friend_requests`** table, keyed on
+  the requester + game + seat with the seen name snapshotted (`RequestInGame`): the shared robot
+  account is never put in `friendships` (so it is not befriended/awaited under its other per-game
+  names and the in-game 🤝 stays pinned to that seat as *sent*), the robot never accepts, the row
+  is not surfaced in Settings → Friends, and a background reaper deletes it once its game has been
+  finished for **7 days**. (Discovery by friend list or platform deep-link is future work.)
 - **Block**: two independent **global** account toggles (`block_chat`,
   `block_friend_requests`) **plus** a **per-user block list**. A per-user block is
   **asymmetric and non-destructive**: the blocker stops receiving everything **from** the