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/lib/codec.ts

@@ -10,7 +10,9 @@ import type { PlacedTile } from './client';
 import type {
   AccountRef,
   BlockList,
+  OutgoingList,
   RobotBlockEntry,
+  RobotFriendRequestEntry,
   Banner,
   BannerCampaign,
   BestMove,
@@ -719,14 +721,25 @@ export function decodeIncomingList(buf: Uint8Array): AccountRef[] {
   return out;
 }
 
-export function decodeOutgoingList(buf: Uint8Array): AccountRef[] {
+export function decodeOutgoingList(buf: Uint8Array): OutgoingList {
   const l = fb.OutgoingRequestList.getRootAsOutgoingRequestList(new ByteBuffer(buf));
-  const out: AccountRef[] = [];
+  const requests: AccountRef[] = [];
   for (let i = 0; i < l.requestsLength(); i++) {
     const r = l.requests(i);
-    if (r) out.push(decodeAccountRef(r));
+    if (r) requests.push(decodeAccountRef(r));
   }
-  return out;
+  const robots: RobotFriendRequestEntry[] = [];
+  for (let i = 0; i < l.robotsLength(); i++) {
+    const r = l.robots(i);
+    if (r)
+      robots.push({
+        id: r.id() ?? '',
+        displayName: r.displayName() ?? '',
+        gameId: r.gameId() ?? '',
+        seat: r.seat(),
+      });
+  }
+  return { requests, robots };
 }
 
 export function decodeBlockList(buf: Uint8Array): BlockList {