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.

ui/src/lib/share.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+import { pickGcgDelivery } from './share';
+
+const file = {} as File;
+
+describe('pickGcgDelivery', () => {
+  it('shares when the platform can share files', () => {
+    expect(pickGcgDelivery({ canShare: () => true, share: async () => {} }, file)).toBe('share');
+  });
+
+  it('downloads when the platform cannot share files', () => {
+    expect(pickGcgDelivery({ canShare: () => false, share: async () => {} }, file)).toBe('download');
+  });
+
+  it('downloads when there is no navigator', () => {
+    expect(pickGcgDelivery(undefined, file)).toBe('download');
+  });
+
+  it('downloads when the Web Share API is incomplete', () => {
+    expect(pickGcgDelivery({ canShare: () => true } as never, file)).toBe('download');
+  });
+});