fix(wallet-switch): late-fail revert, shutdown-freeze, per-wallet PIN gate

The two deferred audit MEDs + the per-wallet PIN follow-up:

- Late-init failure revert (MED): the 1.5s start grace only catches a wallet that
  fails IMMEDIATELY. A wallet that fails LATE in dragonxd init (past the grace)
  used to persist as a broken active_wallet_file. Now a switch stays
  "pending confirm" until the daemon actually connects (onConnected clears it);
  if the connect loop instead hits the crash-wedge (crashCount >= 3) while a
  switch is pending, it flags the main-thread revert (which also resets the crash
  count so the restored wallet can start).
- Shutdown freeze (MED): the switch worker's 30s daemon-stop wait now breaks
  promptly when shutdown starts, so beginShutdown's join of the switch task can't
  freeze the UI for the full 30s (shutdown stops the daemon itself). The seed-
  adopt task is intentionally left to finish (fund-safety), as before.
- Per-wallet PIN (follow-up): App::hasPinVault() (and the lock-screen path) now
  gate on the per-wallet vault presence alone, not the GLOBAL getPinEnabled flag —
  so disabling PIN on one wallet no longer suppresses another wallet's PIN
  quick-unlock after a switch.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -740,6 +740,10 @@ private:
     // wallet_switch_prev_file_ (settings writes stay on the main thread) so a broken wallet isn't
     // persisted across restarts. daemon_restarting_ stays set until the revert re-arms the reconnect.
     std::atomic<bool> wallet_switch_failed_{false};
+    // True from a switch until the new wallet's daemon actually connects (onConnected). If the daemon
+    // instead crash-wedges (a wallet that fails LATE in init, past the fast start grace), the connect
+    // loop flags a revert so a broken wallet still can't stick.
+    std::atomic<bool> wallet_switch_pending_confirm_{false};
     std::string wallet_switch_prev_file_;
 
     // Set by the deleteBlockchainData worker (item count); the main loop surfaces a completion toast