Stage 8 polish: profile validation, finished-game UI, badge + Safari fixes

Owner-review follow-up on the Stage 8 branch:
- Friend code is copyable (📋 + toast). The lobby notification badge is fixed —
  it had inherited the hamburger-bar style — into a proper round count dot.
- Safari: min-width:0 on flex text inputs (friend code, profile, chat) so they
  shrink instead of pushing the adjacent button off-screen.
- Profile editing is validated on both the UI and the backend: display-name format
  (letters joined by single space/./_ separators, no leading/trailing/adjacent
  separators, <=32 runes), a UTC-offset timezone picker (account.ResolveZone parses
  ±HH:MM or a legacy IANA name), a 10-minute away grid capped at 12h (wrap-aware),
  and email format; Save is disabled and invalid fields red-bordered until valid.
  Language stays in Settings.
- In a game, an "add to friends" menu item flips to a disabled "request sent"; chat
  send/nudge became ⬆️/🛎️ icon buttons.
- A finished game drops its last-word highlight, hides Check word / Drop game,
  disables zoom, and draws an inert (greyed) footer instead of hiding it.

Tests: account validators (name/away/zone), UI profileValidation, e2e for the
finished-game footer/menu and the copy control. Docs (PLAN, ARCHITECTURE,
FUNCTIONAL +ru, UI_DESIGN) updated for the display-name rule, UTC-offset timezone
and the 12h away window.

ui/src/components/Menu.svelte

@@ -6,6 +6,7 @@
     label: string;
     onclick: () => void;
     badge?: number;
+    disabled?: boolean;
   }
   let { items, badge = 0 }: { items: MenuItem[]; badge?: number } = $props();
   let open = $state(false);
@@ -27,7 +28,7 @@
     <div class="backdrop" onclick={() => (open = false)}></div>
     <div class="dropdown">
       {#each items as it (it.label)}
-        <button onclick={() => pick(it.onclick)}>
+        <button onclick={() => pick(it.onclick)} disabled={it.disabled}>
           <span>{it.label}</span>
           {#if it.badge}<span class="idot">{it.badge}</span>{/if}
         </button>
@@ -82,7 +83,7 @@
     text-align: center;
     font-weight: 700;
   }
-  .burger span {
+  .burger span:not(.dot) {
     display: block;
     height: 3px;
     background: var(--text);
@@ -120,7 +121,11 @@
     user-select: none;
     -webkit-user-select: none;
   }
-  .dropdown button:hover {
+  .dropdown button:hover:not(:disabled) {
     background: var(--surface-2);
   }
+  .dropdown button:disabled {
+    color: var(--text-muted);
+    opacity: 0.6;
+  }
 </style>