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>

res/lang/zh.json

@@ -485,6 +485,17 @@
     "download_bootstrap": "下载引导程序",
     "dragonx_green": "DragonX（绿色）",
     "edit": "编辑",
+    "empty_wallet_keys_suffix": "个密钥",
+    "empty_wallet_open_manager": "打开钱包管理器",
+    "empty_wallet_restore": "恢复我的钱包",
+    "empty_wallet_salvage_body": "此钱包为空，因为先前的一次自动修复已将您的原始钱包作为备份保存到一旁。您的币几乎肯定在该备份中，并未丢失。恢复它即可重新加载您的资金——不会删除任何内容；当前文件会先被保存到一旁。",
+    "empty_wallet_salvage_headline": "您的币安全地存放在备份文件中。",
+    "empty_wallet_salvage_title": "您的钱包可能已被修复",
+    "empty_wallet_warning_body": "此钱包没有地址也没有资金，但您的 DragonX 文件夹中的另一个钱包文件包含密钥。您的币很可能在其中，并未丢失。打开钱包管理器以切换到持有您资金的钱包。",
+    "empty_wallet_warning_dismiss": "不再为此钱包提示",
+    "empty_wallet_warning_dismiss_tip": "仅对当前钱包文件停止此提示。如果您以后切换到另一个空钱包，可能会再次提示。",
+    "empty_wallet_warning_headline": "您可能打开了错误的钱包。",
+    "empty_wallet_warning_title": "此钱包为空",
     "enc_confirm": "确认：",
     "enc_desc": "加密钱包会用密码短语保护您的私钥。加密后，守护进程将重新启动。",
     "enc_encrypting": "正在加密钱包...",