Stage 17 #5: hide finished games from your own lobby list

A player can remove a finished game from their own 'my games' list. The action is
per-account, finished-only and irreversible (the game stays for the other players;
there is no un-hide).

- backend: migration 00012 game_hidden(account_id, game_id); store HideGame +
  hiddenGameIDs + ListGamesForAccount filtering; service HideGame (seat + finished
  checks, reusing ErrNotAPlayer / ErrGameActive); POST /api/v1/user/games/:id/hide.
- gateway: game.hide edge op (reuses GameActionRequest -> Ack) + backendclient.HideGame.
- ui: finished rows reveal a delete via swipe-left (touch) or a kebab tap (desktop),
  active rows get an inert chevron for icon alignment; optimistic removal + lobby-cache
  sync; mock + transport + client wiring; lobby.hideGame label (en/ru).
- tests: integration (active->ErrGameActive, outsider->ErrNotAPlayer, per-account,
  idempotent), gateway transcode round-trip, mock e2e (kebab -> delete); hardened a
  pre-existing chat-screen .back transition flake surfaced by the new test's timing.
- docs: ARCHITECTURE persistence list, FUNCTIONAL (+ _ru) lobby story, PLAN tracker.

backend/internal/inttest/hide_test.go

@@ -0,0 +1,67 @@
+//go:build integration
+
+package inttest
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/google/uuid"
+
+	"scrabble/backend/internal/game"
+)
+
+// TestHideFinishedGame covers Stage 17 per-account game hiding: an active game cannot be
+// hidden, a finished game is removed from the hider's own list while staying visible to the
+// other player, an outsider cannot hide it, and the action is idempotent.
+func TestHideFinishedGame(t *testing.T) {
+	ctx := context.Background()
+	svc, gameID, seats, _ := newDraftGame(t)
+
+	// Hiding while the game is still active is refused.
+	if err := svc.HideGame(ctx, seats[0], gameID); !errors.Is(err, game.ErrGameActive) {
+		t.Fatalf("hide active = %v, want ErrGameActive", err)
+	}
+
+	// Finish the game by seat 0 resigning.
+	if _, err := svc.Resign(ctx, gameID, seats[0]); err != nil {
+		t.Fatalf("resign: %v", err)
+	}
+
+	// A non-player cannot hide it.
+	if err := svc.HideGame(ctx, provisionAccount(t), gameID); !errors.Is(err, game.ErrNotAPlayer) {
+		t.Fatalf("hide by outsider = %v, want ErrNotAPlayer", err)
+	}
+
+	// Seat 0 hides the finished game; hiding again is a no-op success.
+	if err := svc.HideGame(ctx, seats[0], gameID); err != nil {
+		t.Fatalf("hide: %v", err)
+	}
+	if err := svc.HideGame(ctx, seats[0], gameID); err != nil {
+		t.Fatalf("hide twice: %v", err)
+	}
+
+	// It is gone from seat 0's list but still in seat 1's (hiding is per-account).
+	if containsGame(t, svc, seats[0], gameID) {
+		t.Error("hidden game still listed for the hider")
+	}
+	if !containsGame(t, svc, seats[1], gameID) {
+		t.Error("hidden game should remain listed for the other player")
+	}
+}
+
+// containsGame reports whether the account's lobby list includes gameID.
+func containsGame(t *testing.T, svc *game.Service, accountID, gameID uuid.UUID) bool {
+	t.Helper()
+	games, err := svc.ListForAccount(context.Background(), accountID)
+	if err != nil {
+		t.Fatalf("list for account: %v", err)
+	}
+	for _, g := range games {
+		if g.ID == gameID {
+			return true
+		}
+	}
+	return false
+}