Stage 8: UI social/account/history surfaces

Wire the deferred Stage 7 surfaces end-to-end (UI -> gateway transcode ->
backend REST -> existing domain services): friends (incl. one-time friend
codes), per-user blocks, friend-game invitations, profile editing + email
binding, the statistics screen, and the in-game history + GCG export.

Friends gain two add paths (interview decision, a deliberate plan change):
one-time 6-digit codes (friend_codes table, 12h TTL, single-use, rate-limited
redeem); and play-gated requests (shared game required) where an explicit
decline is permanent, an ignored request lapses after 30 days, and a code
bypasses a decline. Migration 00006 widens friendships_status_chk and adds
friend_codes.

Lobby notification badge is poll + push: a new generic `notify` event drives
it live; the client polls on open/focus. Language stays a single Settings
control that writes through to the durable account's preferred_language. GCG
export is finished-only (game.ErrGameActive) and shares/downloads the .gcg file.

Tests: backend unit + inttest (friend gate/decline/code, ListInvitations,
GetStats, GCG gate), gateway transcode round-trips + notify constructor, UI
vitest (codecs, win-rate, share choice) + Playwright social specs. Docs: PLAN
(Stage 8 done + refinements + TODO-5), ARCHITECTURE, FUNCTIONAL(+ru), UI_DESIGN,
TESTING, module READMEs.

backend/internal/inttest/social_test.go

@@ -43,7 +43,9 @@ func newGameWithSeats(t *testing.T, n int) (uuid.UUID, []uuid.UUID) {
 func TestFriendRequestLifecycle(t *testing.T) {
 	ctx := context.Background()
 	svc := newSocialService()
-	a, b := provisionAccount(t), provisionAccount(t)
+	// A request is only allowed between players who share a game.
+	_, seats := newGameWithSeats(t, 2)
+	a, b := seats[0], seats[1]
 
 	if err := svc.SendFriendRequest(ctx, a, b); err != nil {
 		t.Fatalf("send: %v", err)
@@ -102,7 +104,8 @@ func TestFriendRequestRefusedByToggleAndBlock(t *testing.T) {
 func TestBlockSeversFriendship(t *testing.T) {
 	ctx := context.Background()
 	svc := newSocialService()
-	a, b := provisionAccount(t), provisionAccount(t)
+	_, seats := newGameWithSeats(t, 2)
+	a, b := seats[0], seats[1]
 	if err := svc.SendFriendRequest(ctx, a, b); err != nil {
 		t.Fatalf("send: %v", err)
 	}
@@ -117,6 +120,113 @@ func TestBlockSeversFriendship(t *testing.T) {
 	}
 }
 
+func TestFriendRequestRequiresSharedGame(t *testing.T) {
+	ctx := context.Background()
+	svc := newSocialService()
+	a, b := provisionAccount(t), provisionAccount(t) // never played together
+	if err := svc.SendFriendRequest(ctx, a, b); !errors.Is(err, social.ErrNoSharedGame) {
+		t.Fatalf("send without shared game = %v, want ErrNoSharedGame", err)
+	}
+}
+
+func TestFriendDeclineIsPermanentUntilCode(t *testing.T) {
+	ctx := context.Background()
+	svc := newSocialService()
+	_, seats := newGameWithSeats(t, 2)
+	a, b := seats[0], seats[1]
+
+	if err := svc.SendFriendRequest(ctx, a, b); err != nil {
+		t.Fatalf("send: %v", err)
+	}
+	if err := svc.RespondFriendRequest(ctx, b, a, false); err != nil { // b declines a
+		t.Fatalf("decline: %v", err)
+	}
+	// An explicit decline is remembered: a cannot re-send.
+	if err := svc.SendFriendRequest(ctx, a, b); !errors.Is(err, social.ErrRequestDeclined) {
+		t.Fatalf("resend after decline = %v, want ErrRequestDeclined", err)
+	}
+	// But a one-time code from b bypasses the decline.
+	code, err := svc.IssueFriendCode(ctx, b)
+	if err != nil {
+		t.Fatalf("issue code: %v", err)
+	}
+	issuer, err := svc.RedeemFriendCode(ctx, a, code.Code)
+	if err != nil {
+		t.Fatalf("redeem: %v", err)
+	}
+	if issuer != b {
+		t.Fatalf("redeem issuer = %s, want b", issuer)
+	}
+	if friends, _ := svc.ListFriends(ctx, a); len(friends) != 1 || friends[0] != b {
+		t.Fatalf("friends of a after code = %v, want [b]", friends)
+	}
+}
+
+func TestFriendRequestResendAfterExpiry(t *testing.T) {
+	ctx := context.Background()
+	svc := newSocialService()
+	_, seats := newGameWithSeats(t, 2)
+	a, b := seats[0], seats[1]
+	if err := svc.SendFriendRequest(ctx, a, b); err != nil {
+		t.Fatalf("send: %v", err)
+	}
+	// A request older than the 30-day window lazily expires: it leaves the incoming
+	// list and may be re-sent.
+	if _, err := testDB.ExecContext(ctx,
+		`UPDATE backend.friendships SET created_at = now() - interval '31 days' WHERE requester_id = $1 AND addressee_id = $2`, a, b); err != nil {
+		t.Fatalf("backdate: %v", err)
+	}
+	if got, _ := svc.ListIncomingRequests(ctx, b); len(got) != 0 {
+		t.Fatalf("expired request still incoming: %v", got)
+	}
+	if err := svc.SendFriendRequest(ctx, a, b); err != nil {
+		t.Fatalf("resend after expiry: %v", err)
+	}
+	if got, _ := svc.ListIncomingRequests(ctx, b); len(got) != 1 || got[0] != a {
+		t.Fatalf("re-sent request not incoming: %v", got)
+	}
+}
+
+func TestFriendCodeSelfAndSingleUse(t *testing.T) {
+	ctx := context.Background()
+	svc := newSocialService()
+	a := provisionAccount(t)
+	code, err := svc.IssueFriendCode(ctx, a)
+	if err != nil {
+		t.Fatalf("issue: %v", err)
+	}
+	if _, err := svc.RedeemFriendCode(ctx, a, code.Code); !errors.Is(err, social.ErrSelfRelation) {
+		t.Fatalf("self redeem = %v, want ErrSelfRelation", err)
+	}
+	b := provisionAccount(t)
+	if _, err := svc.RedeemFriendCode(ctx, b, code.Code); err != nil {
+		t.Fatalf("redeem: %v", err)
+	}
+	// Single-use: redeeming the same code again fails.
+	if _, err := svc.RedeemFriendCode(ctx, provisionAccount(t), code.Code); !errors.Is(err, social.ErrFriendCodeInvalid) {
+		t.Fatalf("reused code = %v, want ErrFriendCodeInvalid", err)
+	}
+	if friends, _ := svc.ListFriends(ctx, b); len(friends) != 1 || friends[0] != a {
+		t.Fatalf("friends of b = %v, want [a]", friends)
+	}
+}
+
+func TestListBlocks(t *testing.T) {
+	ctx := context.Background()
+	svc := newSocialService()
+	a, b := provisionAccount(t), provisionAccount(t)
+	if err := svc.Block(ctx, a, b); err != nil {
+		t.Fatalf("block: %v", err)
+	}
+	blocked, err := svc.ListBlocks(ctx, a)
+	if err != nil {
+		t.Fatalf("list blocks: %v", err)
+	}
+	if len(blocked) != 1 || blocked[0] != b {
+		t.Fatalf("blocks = %v, want [b]", blocked)
+	}
+}
+
 func TestChatPostListAndBlocks(t *testing.T) {
 	ctx := context.Background()
 	svc := newSocialService()