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.

pkg/fbs/scrabblefb/OutgoingRequestList.go

@@ -61,8 +61,28 @@ func (rcv *OutgoingRequestList) RequestsLength() int {
 	return 0
 }
 
+func (rcv *OutgoingRequestList) Robots(obj *RobotFriendRef, j int) bool {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		x := rcv._tab.Vector(o)
+		x += flatbuffers.UOffsetT(j) * 4
+		x = rcv._tab.Indirect(x)
+		obj.Init(rcv._tab.Bytes, x)
+		return true
+	}
+	return false
+}
+
+func (rcv *OutgoingRequestList) RobotsLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
 func OutgoingRequestListStart(builder *flatbuffers.Builder) {
-	builder.StartObject(1)
+	builder.StartObject(2)
 }
 func OutgoingRequestListAddRequests(builder *flatbuffers.Builder, requests flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(requests), 0)
@@ -70,6 +90,12 @@ func OutgoingRequestListAddRequests(builder *flatbuffers.Builder, requests flatb
 func OutgoingRequestListStartRequestsVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
 	return builder.StartVector(4, numElems, 4)
 }
+func OutgoingRequestListAddRobots(builder *flatbuffers.Builder, robots flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(robots), 0)
+}
+func OutgoingRequestListStartRobotsVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
 func OutgoingRequestListEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }