Stage 17 round 6 (#16/#17, PR C): lobby sort + server-derived in-game friend state

Lobby: group the my-games list into your-turn / opponent-turn / finished
(empty sections hidden), ordered by last activity (your-turn oldest-first,
the other two newest-first), as a compact line-separated list. gameDTO and
FB GameView gain last_activity_unix (turn start while active, finish time
once finished); a pure lib/lobbysort.ts holds the grouping/ordering.

Friends: the in-game 'add to friends' item is now server-derived via a new
GET /user/friends/outgoing (+ friends.outgoing op), returning addressees with
a pending OR declined request (both read as 'request sent'), so it is correct
across reloads; it shows a disabled '✓ in friends' once accepted. It
live-updates when the opponent answers: RespondFriendRequest now publishes
friend_added (accept) / friend_declined (new notify sub-kind, decline) to the
original requester, whose open game re-derives its friend state.

Tests: lobbysort unit test; gateway outgoing + last_activity transcode tests;
backend integration ListOutgoingRequests + respond-publishes-to-requester;
e2e updated for the new lobby section labels + a non-friend active opponent.
Docs: ARCHITECTURE notify catalog, FUNCTIONAL(+ru) lobby/friends, PLAN.

pkg/fbs/scrabble.fbs

@@ -66,6 +66,9 @@ table GameView {
   move_count:int;
   end_reason:string;
   seats:[SeatView];
+  // last_activity_unix is the lobby sort key: the current turn's start for an active
+  // game, the finish time for a finished one (Stage 17).
+  last_activity_unix:long;
 }
 
 // MoveRecord is one decoded move (a committed play, or a hint preview).
@@ -389,6 +392,13 @@ table IncomingRequestList {
   requests:[AccountRef];
 }
 
+// OutgoingRequestList is the accounts the caller has already requested and cannot
+// (re-)request: a live pending request or one the addressee declined. The game's
+// "add to friends" item reads it to stay disabled across reloads (Stage 17).
+table OutgoingRequestList {
+  requests:[AccountRef];
+}
+
 // FriendCode is a freshly issued one-time add-a-friend code (returned once).
 table FriendCode {
   code:string;
@@ -492,8 +502,9 @@ table MatchFoundEvent {
 
 // NotificationEvent is a lightweight "something changed, re-poll" signal that
 // drives the lobby badge (incoming friend requests, invitations). kind is a sub-
-// discriminator ("friend_request", "friend_added", "invitation", "game_started");
-// the client re-fetches its lobby counters on any of them.
+// discriminator ("friend_request", "friend_added", "friend_declined", "invitation",
+// "game_started"); the client re-fetches its lobby counters (and, for a requester
+// watching a game, its friend state) on any of them.
 table NotificationEvent {
   kind:string;
 }