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/FUNCTIONAL.md

@@ -207,7 +207,10 @@ Blocking an **auto-match opponent who is secretly a robot** behaves the same in
 (struck name, hidden composer) and lists the blocked opponent under the name you saw, but is
 recorded only against that game — the disguise holds, the shared robot is never globally
 blocked, and the matchmaker keeps pairing you with robots (so you can never block yourself out
-of opponents). Per-game chat is for quick reactions: messages are short
+of opponents). Sending the 🤝 to such a **disguised robot** likewise records the request only
+against that game (pinned to the seat, so it stays *sent* there without touching that robot in
+your other games); the robot **ignores it**, the request never appears in **Settings → Friends**,
+and it drops automatically about a week after the game ends. Per-game chat is for quick reactions: messages are short
 (up to 60 characters) and may not contain links, email addresses or phone numbers,
 even disguised. You may send **one message per turn, on your own turn**; once it is sent
 the field gives way to a short caption until your next turn. Nudge the player whose turn