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.test.ts

@@ -256,7 +256,7 @@ describe('codec', () => {
     expect(gl.atGameLimit).toBe(true);
   });
 
-  it('decodes an OutgoingRequestList of account refs', () => {
+  it('decodes an OutgoingRequestList of account refs plus per-game robot requests', () => {
     const b = new Builder(128);
     const id = b.createString('o-1');
     const dn = b.createString('Pat');
@@ -264,11 +264,20 @@ describe('codec', () => {
     fb.AccountRef.addAccountId(b, id);
     fb.AccountRef.addDisplayName(b, dn);
     const ref = fb.AccountRef.endAccountRef(b);
-    const vec = fb.OutgoingRequestList.createRequestsVector(b, [ref]);
+    const reqVec = fb.OutgoingRequestList.createRequestsVector(b, [ref]);
+    const rid = b.createString('r-1');
+    const rdn = b.createString('Robbie');
+    const rgid = b.createString('g-1');
+    const robot = fb.RobotFriendRef.createRobotFriendRef(b, rid, rdn, rgid, 1);
+    const robVec = fb.OutgoingRequestList.createRobotsVector(b, [robot]);
     fb.OutgoingRequestList.startOutgoingRequestList(b);
-    fb.OutgoingRequestList.addRequests(b, vec);
+    fb.OutgoingRequestList.addRequests(b, reqVec);
+    fb.OutgoingRequestList.addRobots(b, robVec);
     b.finish(fb.OutgoingRequestList.endOutgoingRequestList(b));
-    expect(decodeOutgoingList(b.asUint8Array())).toEqual([{ accountId: 'o-1', displayName: 'Pat' }]);
+    expect(decodeOutgoingList(b.asUint8Array())).toEqual({
+      requests: [{ accountId: 'o-1', displayName: 'Pat' }],
+      robots: [{ id: 'r-1', displayName: 'Robbie', gameId: 'g-1', seat: 1 }],
+    });
   });
 
   it('encodes a TargetRequest', () => {