feat(offline): hotseat creation roster + host-participate flow

NewGame offline 'with friends' now builds a local pass-and-play game:
- lib/roster.ts: keep-last-valid name + roster->seats (unit-tested).
- NewGame.svelte: master host-PIN gate (rows disabled until set),
  'are you playing too?' prompt seating the host at row 0, 2-4 player
  rows with inline name validation + optional per-seat PIN, add/remove
  (remove behind the master PIN), variant + multiple-words, Start.
- PinPad: verification via a verify(pin) callback (UI-held lock at
  creation, source-held in-game) instead of a lock prop.
- i18n: hotseat.* (en + ru); the offline mode selector is now shown offline.

ui/src/components/PinPad.svelte

@@ -2,15 +2,17 @@
   // Apple-lock-screen-style 4-digit PIN pad for offline pass-and-play (hotseat) games.
   // Modes:
   //   set     — enter a PIN, then repeat it to confirm; emits { kind: 'set', lock }.
-  //   verify  — enter a PIN; auto-checks against `lock` on the 4th digit; emits
-  //             { kind: 'verified' } or shakes + clears on a wrong PIN.
-  //   change  — verify the current PIN (against `lock`), then offer "set a new PIN"
-  //             (the set flow) or, when allowRemove, "remove PIN" ({ kind: 'removed' }).
-  // The pad never shows an OK button: entering the 4th digit is the action. PIN storage
-  // is a social lock, not cryptography — see lib/pin.ts.
+  //   verify  — enter a PIN; runs `verify(pin)` on the 4th digit; emits { kind: 'verified' }
+  //             or shakes + clears on a wrong PIN.
+  //   change  — run `verify` on the current PIN, then offer "set a new PIN" (the set flow)
+  //             or, when allowRemove, "remove PIN" ({ kind: 'removed' }).
+  // Verification is delegated to the caller's `verify` callback: at creation time it checks a
+  // UI-held lock (lib/pin verifyPin); in-game it delegates to the local source (which holds the
+  // stored lock). The pad never shows an OK button: entering the 4th digit is the action. PIN
+  // storage is a social lock, not cryptography — see lib/pin.ts.
   import Modal from './Modal.svelte';
   import { t } from '../lib/i18n/index.svelte';
-  import { newLock, verifyPin, type PinLock } from '../lib/pin';
+  import { newLock, type PinLock } from '../lib/pin';
 
   /** PinResult is the outcome handed to onresult when the pad completes. */
   export type PinResult =
@@ -21,14 +23,15 @@
   let {
     mode,
     title = '',
-    lock,
+    verify,
     allowRemove = false,
     onclose,
     onresult,
   }: {
     mode: 'set' | 'verify' | 'change';
     title?: string;
-    lock?: PinLock;
+    /** Verifies an entered PIN (required for 'verify' and 'change'). */
+    verify?: (pin: string) => Promise<boolean>;
     allowRemove?: boolean;
     onclose?: () => void;
     onresult: (r: PinResult) => void;
@@ -70,13 +73,13 @@
     busy = true;
     try {
       if (phase === 'old') {
-        if (lock && (await verifyPin(buffer, lock))) {
+        if (verify && (await verify(buffer))) {
           buffer = '';
           error = false;
           phase = 'menu';
         } else fail();
       } else if (phase === 'enter' && mode === 'verify') {
-        if (lock && (await verifyPin(buffer, lock))) onresult({ kind: 'verified' });
+        if (verify && (await verify(buffer))) onresult({ kind: 'verified' });
         else fail();
       } else if (phase === 'enter') {
         first = buffer;