fix: security-audit remediation (15 findings), empty-wallet warning, and send/chat/console/shutdown UX

Security audit remediation (15 confirmed findings from the codebase audit):
- H-02: scrub+delete the decrypt-flow plaintext key export on ALL exit paths
  (RAII guard) and purge stale obsidiandecryptexport* files at startup.
- M-01/L-03/L-04/L-05/L-07: sodium_memzero the Set-PIN and encrypt-PIN worker
  passphrase/PIN copies, the RPC Basic-auth string (auth_), the exported/imported
  key buffers (App::wipeSecrets, called from ~App and before main's _Exit), and
  the first-run wizard "Skip" buffers.
- M-03/M-04/M-05/L-06: return locked COPIES from XmrigManager/EmbeddedDaemon
  getters (dedicated error_mutex_; DaemonController::lastError now by value),
  route xmrig last_error_ writes through a locked setter, and wrap
  shutdown_status_/wizard_stop_status_ in a locking GuardedStatus
  (wizard_stopping_external_ -> std::atomic).
- M-02: persist after a console send/shield/import in the lite backend.
- L-01: require the confirm click for z_shieldcoinbase/z_mergetoaddress.
- L-02: quote/escape each Windows daemon argv per the MSDN CommandLineToArgvW rules.
- L-08: pin json/tomlplusplus/libwebp FetchContent to immutable commit SHAs.
- I-01: extract updater archives from the already-verified in-memory buffer
  (no disk re-read TOCTOU).

Feature: warn once (full-node) when the active wallet loads empty while a sibling
wallet file in the datadir holds keys. A funded salvage wallet.<ts>.bak routes to
the recovery/Restore flow; a funded sibling .dat routes to the wallet manager.
Per-wallet-file dismissal; gated on synced + address-list-loaded to avoid false
positives on warm reconnect / spent-down wallets.

UX fixes:
- send: show the TOTAL balance (with a spendable "available" note) in the source
  dropdown and keep pending-change addresses visible.
- chat: insert emoji at the cursor position; restrict new-chat recipients to
  shielded (z) addresses.
- console: optional auto-focus of the command input on tab open (off by default).
- shutdown: when "stop external daemon" is on, keep the shutdown screen up until
  the external node actually exits, showing live status.

Adversarially reviewed; verified across full-node, lite, and Windows builds; tests pass.

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

src/ui/windows/console_command_reference.cpp

@@ -160,10 +160,10 @@ const ConsoleCommandEntry kWalletCommands[] = {
      "z_sendmany \"RfromAddr\" [{\"address\":\"zs1toAddr\",\"amount\":1.0}]", "send pay private shielded transfer money", true},
     {"z_shieldcoinbase", "Shield transparent coinbase funds to a z-address", "\"fromaddress\" \"tozaddress\" [fee] [limit]",
      "Moves newly mined (coinbase) transparent funds into a private shielded z-address, since mined rewards must be shielded before they can be spent normally. Runs in the background and returns an operation id.",
-     "z_shieldcoinbase \"RyourMiningAddr\" \"zs1yourShieldedAddr\"", "shield mining rewards coinbase private hide mined funds move to shielded"},
+     "z_shieldcoinbase \"RyourMiningAddr\" \"zs1yourShieldedAddr\"", "shield mining rewards coinbase private hide mined funds move to shielded", true},
     {"z_mergetoaddress", "Merge multiple UTXOs/notes to one address", "[\"fromaddress\",...] \"toaddress\" [fee] [limit]",
      "Combines many small balances (from transparent and/or shielded addresses) into a single destination address in one transaction, to consolidate funds. Runs in the background and returns an operation id.",
-     "z_mergetoaddress [\"RyourAddr\",\"zs1yourShieldedAddr\"] \"zs1destShieldedAddr\"", "merge combine consolidate funds sweep small balances into one address"},
+     "z_mergetoaddress [\"RyourAddr\",\"zs1yourShieldedAddr\"] \"zs1destShieldedAddr\"", "merge combine consolidate funds sweep small balances into one address", true},
     {"listtransactions", "List recent wallet transactions", "[\"account\"] [count] [from]",
      "Your most recent wallet transactions, newest first \xE2\x80\x94 amounts, addresses and confirmations.",
      "listtransactions", "transactions history recent payments received sent"},