Stage 17 round 5 — backend/correctness bug fixes

- Resign on the opponent's turn: engine ResignSeat(seat) resigns a specific seat
  (not just toMove); game.Resign bypasses the turn check and forfeits the actor's seat.
- Quick-match cancel was a UI no-op (only stopped polling): add the full path
  (REST /lobby/cancel -> gateway lobby.cancel -> client) and clear the matchmaker's
  pending result on Cancel, so a cancelled search is dequeued (no 'already queued', no
  later robot-substituted game). NewGame dequeues on cancel and on abandon.
- Lobby win/loss: result.ts ranked by score, so a 0-0 resignation read as a win.
  The winner now takes rank 1 and the viewer is placed from rank 2 — matching the
  game-detail screen.
- Friend request to a robot: robots no longer block requests; the request stays
  pending and expires (friendRequestTTL), mirroring a human who ignores it.
- Nudge cooldown: ErrNudgeTooSoon now maps to a distinct nudge_too_soon code with a
  correct message; the chat nudge button disables during the hourly cooldown; the
  nudge note reads 'Waiting for your move!' (button keeps the Nudge action label).
Tests: engine/service off-turn resign, matchmaker cancel-clears-result, friend-to-robot
inttest, result.ts 0-0 resignation, nudge_too_soon mapping.

ui/src/lib/result.test.ts

@@ -48,6 +48,15 @@ describe('resultBadge', () => {
     });
   });
 
+  it('finished two-player: a 0-0 resignation is a defeat, not a score-tied win', () => {
+    // The opponent won by resignation (isWinner) although neither side scored — the lobby
+    // must read this as a loss, matching the game-detail screen (Stage 17 regression).
+    expect(resultBadge(game([seat(0, 'me', 0), seat(1, 'a', 0, true)]), 'me')).toEqual({
+      key: 'result.defeat',
+      emoji: '🥈',
+    });
+  });
+
   it('finished four-player: places by score', () => {
     const last = game([seat(0, 'me', 100), seat(1, 'a', 400, true), seat(2, 'b', 300), seat(3, 'c', 200)]);
     expect(resultBadge(last, 'me')).toEqual({ key: 'result.place4', emoji: '🏅' });