fix(security): don't silently leave a wallet unencrypted or unlocked (W2-2, W2-4)

P0-B encryption-integrity cluster.

W2-2: the first-run wizard's "encrypt" stored the passphrase only in memory and let the
user into the app immediately, so a quit/crash or a failed daemon connect before the
deferred encryption applied left the wallet unencrypted with NO record encryption was
ever requested — the user believing it was encrypted. A persisted encryption_pending
settings flag is now set the moment encryption is requested (never the passphrase, only
the fact). refreshWalletEncryptionState() reconciles it on every connect: wallet observed
encrypted -> clear the flag; wallet NOT encrypted while the flag is set and no deferred
encryption is pending/in-flight -> a once-per-session "your wallet is NOT encrypted — open
Settings to finish" warning (the flag stays set, so it recurs each launch until resolved).
The passphrase is deliberately never persisted to auto-complete — surfacing it is the
secure choice.

W2-4: lockWallet()'s continuation only handled success — a failed walletlock RPC silently
left the wallet UNLOCKED (an unfulfilled auto-lock). It now logs and warns once (reset on
the next successful lock) so a failing auto-lock is visible instead of leaving the wallet
exposed.

Touches settings.{h,cpp}, app_wizard.cpp, app_security.cpp, app.h. Not unit-testable at
this layer (RPC/connect-driven state). Build-clean; ctest 1/1. See docs/wallet-hardening.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.h

@@ -1024,6 +1024,8 @@ private:
     double clipboard_clear_deadline_ = 0.0;
     float loading_timer_ = 0.0f;  // spinner animation for loading overlay
     double connect_stall_since_ = 0.0;  // ImGui::GetTime() when the daemon first went "reachable but not ready"; 0 = not stalling (see util/connect_stall.h)
+    bool encryption_incomplete_warned_ = false;  // W2-2: once-per-session guard for the "encryption didn't complete" warning
+    bool lock_failure_warned_ = false;           // W2-4: guard so a repeatedly-failing auto-lock warns once, not every retry
 
     // Current page (sidebar navigation)
     ui::NavPage current_page_ = ui::NavPage::Overview;