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.

docs/FUNCTIONAL.md

@@ -88,9 +88,11 @@ existing friendship). Per-game chat is for quick reactions: messages are short
 even disguised. Nudge the player whose turn is awaited at most once per hour (the
 nudge is part of the game chat); the out-of-app push is delivered via the platform.
 
-### Profile & settings *(Stage 4)*
-Edit language (en/ru), display name, timezone, the daily away window and the block
-toggles, and bind an email by confirm-code: the backend emails a short code that,
+### Profile & settings *(Stage 4 / 8)*
+Edit the display name (letters joined by single space / "." / "_" separators, up to
+32 characters), the timezone (chosen as a UTC offset), the daily away window (on a
+10-minute grid, at most 12 hours, wrapping midnight) and the block toggles, and bind
+an email by confirm-code: the backend emails a short code that,
 once entered, attaches the email to the account (an email already confirmed by
 another account cannot be taken — that is a merge, a later stage). Linked platform
 accounts and merge arrive in Stage 11.