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.ts

@@ -0,0 +1,48 @@
+// GCG export delivery: share on mobile (Web Share API with a file) where supported,
+// otherwise download via a Blob + <a download> on desktop. The Capacitor-native file
+// save lands with the native wrapper; the Web Share path already covers mobile
+// browsers. pickGcgDelivery is the pure decision, unit-tested with a mock navigator.
+
+import type { GcgExport } from './model';
+
+type ShareNav = Pick<Navigator, 'canShare' | 'share'>;
+
+/** pickGcgDelivery decides between the Web Share API and a Blob download for a file. */
+export function pickGcgDelivery(nav: ShareNav | undefined, file: File): 'share' | 'download' {
+  if (
+    nav &&
+    typeof nav.canShare === 'function' &&
+    typeof nav.share === 'function' &&
+    nav.canShare({ files: [file] })
+  ) {
+    return 'share';
+  }
+  return 'download';
+}
+
+/** shareOrDownloadGcg shares the GCG file where supported, else triggers a download. */
+export async function shareOrDownloadGcg(gcg: GcgExport): Promise<void> {
+  const file = new File([gcg.content], gcg.filename, { type: 'application/x-gcg' });
+  const nav = typeof navigator !== 'undefined' ? navigator : undefined;
+  if (pickGcgDelivery(nav, file) === 'share' && nav) {
+    try {
+      await nav.share({ files: [file], title: gcg.filename });
+      return;
+    } catch {
+      // The user cancelled or sharing failed — fall back to a download.
+    }
+  }
+  downloadFile(gcg.content, gcg.filename);
+}
+
+function downloadFile(content: string, filename: string): void {
+  if (typeof document === 'undefined') return;
+  const url = URL.createObjectURL(new Blob([content], { type: 'application/x-gcg' }));
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = filename;
+  document.body.appendChild(a);
+  a.click();
+  a.remove();
+  URL.revokeObjectURL(url);
+}