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/util/i18n.cpp

@@ -223,6 +223,7 @@ void I18n::loadBuiltinEnglish()
         strings_["chat_send"] = "Send";
         strings_["chat_new_title"] = "New chat";
         strings_["chat_new_zaddr"] = "Recipient z-address";
+        strings_["chat_new_needs_zaddr"] = "Chat needs a shielded (z) address — transparent (t) addresses can't receive encrypted messages.";
         strings_["chat_new_message"] = "Message";
         strings_["chat_new_send"] = "Send request";
         strings_["chat_cancel"] = "Cancel";
@@ -1194,6 +1195,19 @@ void I18n::loadBuiltinEnglish()
         strings_["block_db_reindex_started"] = "Rebuilding the block database from your blocks — this can take a while.";
 
         // Wallet auto-recovery warning (the node moved wallet.dat aside and loaded a salvaged copy).
+        // Empty-active-wallet-with-funded-sibling warning (App::renderEmptyWalletWarningDialog).
+        strings_["empty_wallet_warning_title"] = "This wallet is empty";
+        strings_["empty_wallet_warning_headline"] = "You may have opened the wrong wallet.";
+        strings_["empty_wallet_warning_body"] = "This wallet has no addresses and no funds, but another wallet file in your DragonX folder holds keys. Your coins are most likely in it, not lost. Open the wallet manager to switch to the wallet that holds your funds.";
+        strings_["empty_wallet_keys_suffix"] = "keys";
+        strings_["empty_wallet_open_manager"] = "Open wallet manager";
+        strings_["empty_wallet_warning_dismiss"] = "Don't warn again for this wallet";
+        strings_["empty_wallet_warning_dismiss_tip"] = "Stops this warning for the current wallet file only. If you switch to a different empty wallet later, it can warn again.";
+        // Salvage-backup variant of the same modal (a funded wallet.<ts>.bak from an earlier auto-repair).
+        strings_["empty_wallet_salvage_title"] = "Your wallet may have been repaired";
+        strings_["empty_wallet_salvage_headline"] = "Your coins are safe in a backup file.";
+        strings_["empty_wallet_salvage_body"] = "This wallet is empty because an earlier automatic repair set your original wallet aside as a backup. Your coins are almost certainly in that backup, not lost. Restore it to load your funds again — nothing is deleted; the current file is kept aside first.";
+        strings_["empty_wallet_restore"] = "Restore my wallet";
         strings_["wallet_recovered_title"] = "Your wallet file needs a quick repair";
         strings_["wallet_recovered_safety"] = "Your coins are safe.";
         strings_["wallet_recovered_warn"] = "When the app started, it found that your wallet file didn't pass its consistency check — this usually happens after an app update or an unclean shutdown. The app already protected your data: it set the old file aside and loaded a repaired copy so you're not stuck.";
@@ -1616,6 +1630,8 @@ void I18n::loadBuiltinEnglish()
         strings_["console_zoom_out"] = "Zoom out";
         strings_["console_toggle_accents"] = "Toggle line color accents";
         strings_["console_toggle_text_color"] = "Toggle line text colors";
+        strings_["console_auto_focus"] = "Focus input on open";
+        strings_["console_toggle_auto_focus"] = "Place the cursor in the command box when you open the Console tab";
         strings_["console_accents"] = "Color accents";
         strings_["console_text_colors"] = "Text colors";
         strings_["console_cat_control"] = "Control";
@@ -2123,6 +2139,7 @@ void I18n::loadBuiltinEnglish()
         strings_["send_recipient"] = "RECIPIENT";
         strings_["send_select_source"] = "Select a source address...";
         strings_["send_sending_from"] = "SENDING FROM";
+        strings_["send_available_note"] = "available";
         strings_["send_submitting"] = "Submitting transaction...";
         strings_["send_switch_to_receive"] = "Switch to Receive to get your address and start receiving funds.";
         strings_["send_tooltip_enter_amount"] = "Enter an amount to send";