feat(hint): persist the vs_ai idle-hint wait (wall-clock + read sanitiser)

Per the owner's call, the idle-hint gate now PERSISTS across leaving and reopening the
app, instead of the session-scoped monotonic clock: the unlock is a wall-clock instant
(hintUnlockAtMs) stamped from the robot's reply, stored on the local record, carried on
the game view + the opponent_moved move delta, and read through a sanitiser that caps it
at now + the window. So:
- the wait survives a relaunch (a stuck turn is not forgotten);
- a device clock set BACK cannot freeze the gate (the cap bounds the remaining to the
  window and self-heals on the next read);
- a clock set FORWARD just opens the hint early -- accepted as harmless for a solo game.

- lib/hints.ts hintGateRemainingMs now takes the unlock instant + clamps to the window.
- localgame: re-add hintUnlockAtMs to the record/meta; stamp it off the robot's reply;
  sanitise on read (a shared hintUnlock helper feeds stateView + the opponent_moved event).
- gamedelta + PushEvent: the move delta carries hintUnlockAtMs so the view stays fresh.
- Game.svelte: hintUnlockAt derives from the view; the tick + lock + toast unchanged.
- offline.spec.ts: also assert the lock survives a reload (the wait persisted).
- Docs FUNCTIONAL(+_ru)/ARCHITECTURE updated (persist + sanitiser, not monotonic-resets).

docs/FUNCTIONAL.md

@@ -220,9 +220,11 @@ personal hint wallet once the per-game allowance is spent. Against the robot
 anti-frustration aid: one unlocks only after the player has been **stuck ~30 minutes
 on a turn** (timed from the robot's last move; the very first move, before the robot
 has played, is exempt). While gated the hint button carries a small **🔒 lock** and a
-tap shows how long remains; the lock lifts live at the mark. The wait uses a steady
-in-app timer, not the device clock — changing the clock cannot open or freeze it
-(though a reload restarts the wait). The game ends when the
+tap shows how long remains; the lock lifts live at the mark. The wait **persists across
+leaving and reopening the app**, so a stuck turn is not forgotten. It stays robust to a
+device clock change: the remaining is capped at the window, so a clock set back cannot
+freeze it, and a clock set forward merely opens the hint early — harmless in a solo game.
+The game ends when the
 bag empties and a player clears their rack, after 6 consecutive scoreless turns,
 by resignation, or by the per-game move timeout (5 minutes to 24 hours, default
 24 hours): a missed turn auto-resigns, except while the player is inside their