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.

ui/src/game/Game.svelte

@@ -932,6 +932,10 @@
   // re-send and disable the 🤝).
   let friends = $state(new Set<string>());
   let requested = $state(new Set<string>());
+  // `requestedRobotSeats` are the seat indices of disguised-robot opponents already requested in
+  // THIS game: a robot request is recorded per game+seat (never the shared robot account), so the
+  // 🤝 disables for just this seat and never leaks across the requester's other games.
+  let requestedRobotSeats = $state(new Set<number>());
   // `blocked` are the opponents the viewer has blocked: their 🤝 and ✖️ controls disappear and
   // their name is struck. Derived from the server so it is correct across reloads and live-updates
   // on a user_blocked / user_unblocked event. `blockedRobotSeats` are the seat indices of blocked
@@ -952,7 +956,8 @@
     try {
       const [fl, out] = await Promise.all([gateway.friendsList(), gateway.friendsOutgoing()]);
       friends = new Set(fl.map((f) => f.accountId));
-      requested = new Set(out.map((f) => f.accountId));
+      requested = new Set(out.requests.map((f) => f.accountId));
+      requestedRobotSeats = new Set(out.robots.filter((r) => r.gameId === id).map((r) => r.seat));
     } catch {
       /* best-effort */
     }
@@ -981,14 +986,17 @@
   // caption update the instant the confirm fires) and roll back to the prior state if the command
   // fails to reach the server. The confirming user_blocked / user_added event then just reconciles
   // the same state in place (no flicker).
-  async function addFriend(accountId: string) {
-    const had = requested.has(accountId);
-    requested = new Set([...requested, accountId]);
+  async function addFriend(s: { accountId: string; seat: number }) {
+    // Optimistically mark this seat requested (disables the 🤝 for both a human and a disguised
+    // robot until the server confirms). The request carries the game id so a robot opponent is
+    // recorded as a per-game request pinned to this seat, not against the shared robot account.
+    const hadSeat = requestedRobotSeats.has(s.seat);
+    requestedRobotSeats = new Set([...requestedRobotSeats, s.seat]);
     try {
-      await gateway.friendRequest(accountId);
+      await gateway.friendRequest(s.accountId, id);
       showToast(t('friends.requestSent'));
     } catch (e) {
-      if (!had) requested = new Set([...requested].filter((id) => id !== accountId));
+      if (!hadSeat) requestedRobotSeats = new Set([...requestedRobotSeats].filter((x) => x !== s.seat));
       handleError(e);
     }
   }
@@ -1118,9 +1126,9 @@
             <span class="addfriend">
               <TapConfirm
                 label={t('friends.addFromGame')}
-                disabled={requested.has(s.accountId)}
+                disabled={requested.has(s.accountId) || requestedRobotSeats.has(s.seat)}
                 onConfirming={(v) => (addConfirm[s.seat] = v)}
-                onconfirm={() => addFriend(s.accountId)}
+                onconfirm={() => addFriend(s)}
               >
                 <span class="fico">🤝</span>
               </TapConfirm>