feat(settings): redesign the remove-encryption (decrypt) modal onto reference design

Migrate App::renderDecryptWalletDialog ("Remove Wallet Encryption") onto the
settings-modal reference design — presentation-only for a fund-critical dialog,
plus one deliberate secret-hygiene addition:

- struct-form BeginOverlayDialog(OverlayDialogSpec{BlurFloat, cardWidth 480,
  idSuffix "decrypt"}) replacing the legacy positional overload
- Phase 0 amber TextWrapped warning -> material::DialogWarningHeader(decrypt_warning)
- drop the redundant Phase 0 Separator
- every rendered-chrome string across all 4 phases (PassphraseEntry / Working /
  Success / Error) -> TR() (14 new decrypt_*/try_again keys added to the English
  source + all 8 res/lang/*.json additively; the button reuses
  settings_remove_encryption, the label reuses change_pass_current, cancel/close reused)
- HARDENING: wipe decrypt_pass_buf_ on BlurFloat dismiss (X/Esc/outside-click),
  mirroring the change-passphrase fix; canClose() gates pOpen so this cannot fire
  during the Working phase

The fund-moving async worker pyramid (unlock -> export -> stop -> backup ->
restart -> re-import, vault/PIN cleanup) is byte-for-byte unchanged; the three
in-worker toast notifications and the "Incorrect passphrase" status are left in
English to avoid touching the fund path (a separate service-layer i18n pass).

Verified: build + ctest + hygiene clean; i18n complete in 8 langs with no format
specifiers and the wallet.dat.encrypted.bak literal preserved; a 3-lens adversarial
review (secret-hygiene / fund-path-untouched / ui-i18n) returned zero findings, with
the fund-path lens proving the async pyramid diffs IDENTICAL against HEAD.

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

res/lang/zh.json

@@ -333,6 +333,19 @@
     "date": "日期",
     "date_label": "日期：",
     "debug_logging": "调试日志",
+    "decrypt_desc": "钱包将被导出，守护进程将使用全新的未加密钱包重新启动，并重新导入所有密钥。根据钱包大小，这可能需要几分钟。",
+    "decrypt_error_title": "解密失败",
+    "decrypt_step_backup": "正在备份加密钱包",
+    "decrypt_step_export": "正在导出钱包密钥",
+    "decrypt_step_restart": "正在重启守护进程",
+    "decrypt_step_stop": "正在停止守护进程",
+    "decrypt_step_unlock": "正在解锁钱包",
+    "decrypt_success_desc": "您的钱包现在未加密。加密钱包的备份已保存为 wallet.dat.encrypted.bak，位于您的数据目录中。",
+    "decrypt_success_title": "钱包解密成功！",
+    "decrypt_title": "移除钱包加密",
+    "decrypt_wait_general": "请稍候。守护进程正在导出密钥、重启并重新导入。这可能需要几分钟。",
+    "decrypt_wait_restart": "正在等待守护进程完成启动...",
+    "decrypt_warning": "这将移除您钱包的加密。您的私钥将以未受保护的方式存储在磁盘上。",
     "delete": "删除",
     "delete_blockchain": "删除区块链",
     "delete_blockchain_confirm": "删除并重新同步",
@@ -1269,6 +1282,7 @@
     "transfer_to": "转账至：",
     "transparent": "透明",
     "transparent_address": "透明地址",
+    "try_again": "重试",
     "tt_addr_url": "在区块浏览器中查看地址的基础 URL",
     "tt_address_book": "管理已保存的地址以快速发送",
     "tt_auto_lock": "在此不活动时间后锁定钱包",