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>

src/util/i18n.cpp

@@ -522,6 +522,21 @@ void I18n::loadBuiltinEnglish()
         strings_["change_pass_current"] = "Current Passphrase:";
         strings_["change_pass_new"] = "New Passphrase:";
         strings_["change_pass_confirm"] = "Confirm New:";
+        // --- Remove-encryption (decrypt) dialog (settings) ---
+        strings_["decrypt_title"] = "Remove Wallet Encryption";
+        strings_["decrypt_warning"] = "This will remove encryption from your wallet. Your private keys will be stored unprotected on disk.";
+        strings_["decrypt_desc"] = "The wallet will be exported, the daemon restarted with a fresh unencrypted wallet, and all keys re-imported. This may take several minutes depending on wallet size.";
+        strings_["decrypt_step_unlock"] = "Unlocking wallet";
+        strings_["decrypt_step_export"] = "Exporting wallet keys";
+        strings_["decrypt_step_stop"] = "Stopping daemon";
+        strings_["decrypt_step_backup"] = "Backing up encrypted wallet";
+        strings_["decrypt_step_restart"] = "Restarting daemon";
+        strings_["decrypt_wait_restart"] = "Waiting for the daemon to finish starting up...";
+        strings_["decrypt_wait_general"] = "Please wait. The daemon is exporting keys, restarting, and re-importing. This may take several minutes.";
+        strings_["decrypt_success_title"] = "Wallet decrypted successfully!";
+        strings_["decrypt_success_desc"] = "Your wallet is now unencrypted. A backup of the encrypted wallet was saved as wallet.dat.encrypted.bak in your data directory.";
+        strings_["decrypt_error_title"] = "Decryption failed";
+        strings_["try_again"] = "Try Again";
         strings_["wiz_confirm"] = "Confirm:";
         strings_["wiz_strength_weak"] = "Weak";
         strings_["wiz_strength_fair"] = "Fair";