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/codec.test.ts

@@ -1,7 +1,15 @@
 import { Builder, ByteBuffer } from 'flatbuffers';
 import { describe, expect, it } from 'vitest';
 import * as fb from '../gen/fbs/scrabblefb';
-import { decodeGameList, decodeSession, encodeSubmitPlay } from './codec';
+import {
+  decodeFriendList,
+  decodeGameList,
+  decodeInvitation,
+  decodeSession,
+  decodeStats,
+  encodeSubmitPlay,
+  encodeTarget,
+} from './codec';
 
 describe('codec', () => {
   it('encodes a SubmitPlayRequest the gateway can read', () => {
@@ -77,4 +85,88 @@ describe('codec', () => {
     expect(gl.games[0].seats[0].displayName).toBe('Ann');
     expect(gl.games[0].seats[0].score).toBe(13);
   });
+
+  it('encodes a TargetRequest', () => {
+    const r = fb.TargetRequest.getRootAsTargetRequest(new ByteBuffer(encodeTarget('a-1')));
+    expect(r.accountId()).toBe('a-1');
+  });
+
+  it('decodes a StatsView', () => {
+    const b = new Builder(64);
+    fb.StatsView.startStatsView(b);
+    fb.StatsView.addWins(b, 7);
+    fb.StatsView.addLosses(b, 4);
+    fb.StatsView.addDraws(b, 1);
+    fb.StatsView.addMaxGamePoints(b, 420);
+    fb.StatsView.addMaxWordPoints(b, 90);
+    b.finish(fb.StatsView.endStatsView(b));
+    expect(decodeStats(b.asUint8Array())).toEqual({
+      wins: 7,
+      losses: 4,
+      draws: 1,
+      maxGamePoints: 420,
+      maxWordPoints: 90,
+    });
+  });
+
+  it('decodes a FriendList of account refs', () => {
+    const b = new Builder(128);
+    const id = b.createString('a-1');
+    const dn = b.createString('Ann');
+    fb.AccountRef.startAccountRef(b);
+    fb.AccountRef.addAccountId(b, id);
+    fb.AccountRef.addDisplayName(b, dn);
+    const ref = fb.AccountRef.endAccountRef(b);
+    const vec = fb.FriendList.createFriendsVector(b, [ref]);
+    fb.FriendList.startFriendList(b);
+    fb.FriendList.addFriends(b, vec);
+    b.finish(fb.FriendList.endFriendList(b));
+    expect(decodeFriendList(b.asUint8Array())).toEqual([{ accountId: 'a-1', displayName: 'Ann' }]);
+  });
+
+  it('decodes an Invitation with inviter and invitees', () => {
+    const b = new Builder(256);
+    const iid = b.createString('u-1');
+    const idn = b.createString('Me');
+    fb.AccountRef.startAccountRef(b);
+    fb.AccountRef.addAccountId(b, iid);
+    fb.AccountRef.addDisplayName(b, idn);
+    const inviter = fb.AccountRef.endAccountRef(b);
+
+    const aid = b.createString('inv-1');
+    const adn = b.createString('Friend');
+    const resp = b.createString('pending');
+    fb.InvitationInvitee.startInvitationInvitee(b);
+    fb.InvitationInvitee.addAccountId(b, aid);
+    fb.InvitationInvitee.addDisplayName(b, adn);
+    fb.InvitationInvitee.addSeat(b, 1);
+    fb.InvitationInvitee.addResponse(b, resp);
+    const invitee = fb.InvitationInvitee.endInvitationInvitee(b);
+    const invitees = fb.Invitation.createInviteesVector(b, [invitee]);
+
+    const id = b.createString('i-1');
+    const variant = b.createString('english');
+    const dropout = b.createString('remove');
+    const status = b.createString('pending');
+    const gid = b.createString('');
+    fb.Invitation.startInvitation(b);
+    fb.Invitation.addId(b, id);
+    fb.Invitation.addInviter(b, inviter);
+    fb.Invitation.addInvitees(b, invitees);
+    fb.Invitation.addVariant(b, variant);
+    fb.Invitation.addTurnTimeoutSecs(b, 86400);
+    fb.Invitation.addHintsAllowed(b, true);
+    fb.Invitation.addHintsPerPlayer(b, 1);
+    fb.Invitation.addDropoutTiles(b, dropout);
+    fb.Invitation.addStatus(b, status);
+    fb.Invitation.addGameId(b, gid);
+    b.finish(fb.Invitation.endInvitation(b));
+
+    const inv = decodeInvitation(b.asUint8Array());
+    expect(inv.id).toBe('i-1');
+    expect(inv.inviter).toEqual({ accountId: 'u-1', displayName: 'Me' });
+    expect(inv.invitees).toHaveLength(1);
+    expect(inv.invitees[0]).toEqual({ accountId: 'inv-1', displayName: 'Friend', seat: 1, response: 'pending' });
+    expect(inv.variant).toBe('english');
+  });
 });