feat(settings): redesign the PIN setup/change/remove modals onto reference design

Migrate the three PIN dialogs in App::renderPinDialogs (Set PIN / Change PIN /
Remove PIN) onto the settings-modal reference design — presentation-only, plus a
deliberate secret-hygiene addition:

- struct-form BeginOverlayDialog(OverlayDialogSpec{BlurFloat, cardWidth 420/420/400,
  idSuffix pinsetup/pinchange/pinremove}) replacing the legacy positional overload
- drop each dialog's redundant post-description Separator
- every rendered-chrome string -> TR(): titles/buttons reuse settings_set_pin /
  settings_change_pin / settings_remove_pin, the Set-PIN confirm reuses
  wiz_pin_confirm; 7 new pin_* keys added to the English source + all 8
  res/lang/*.json additively; ImGui::Text -> TextUnformatted for labels
- HARDENING: wipe the passphrase/PIN input buffers on BlurFloat dismiss
  (X/Esc/outside-click) for all three dialogs. Set PIN's wallet-passphrase buffer
  (pin_passphrase_buf_) was previously left resident on dismiss; it is now zeroed.

The vault/RPC path is byte-for-byte unchanged: the submit-time memsets, the
walletpassphrase/walletlock RPCs, vault_->store/changePin/retrieve/removeVault,
SecureVault::secureZero, and setPinEnabled/save are untouched. The pin_status_ and
toast strings inside the worker callbacks are left in English (a separate
service-layer i18n pass), to avoid editing the secret path.

Verified: build + ctest + hygiene clean; i18n complete in 8 langs with no format
specifiers; a 3-lens adversarial review (secret-hygiene / presentation-only /
ui-i18n) returned zero findings, with the presentation lens proving the vault path
diffs byte-for-byte identical against HEAD.

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

res/lang/es.json

@@ -874,7 +874,14 @@
     "peers_upper": "NODOS",
     "peers_version": "Versión",
     "pending": "Pendiente",
+    "pin_change_desc": "Cambia tu PIN de desbloqueo. Necesitas tu PIN actual y un nuevo PIN.",
+    "pin_confirm_new_label": "Confirmar nuevo PIN:",
+    "pin_current_label": "PIN actual:",
+    "pin_new_label": "Nuevo PIN (4-8 dígitos):",
     "pin_not_set": "PIN no configurado. Use la contraseña para desbloquear.",
+    "pin_remove_desc": "Introduce tu PIN actual para confirmar la eliminación. Necesitarás tu frase de contraseña completa para desbloquear.",
+    "pin_setup_desc": "Establece un PIN de 4-8 dígitos para desbloquear el monedero rápidamente. Tu frase de contraseña se cifrará con este PIN y se almacenará localmente.",
+    "pin_wallet_passphrase": "Frase de contraseña del monedero:",
     "ping": "Ping",
     "portfolio_add_entry": "Añadir entrada",
     "portfolio_add_to": "Agregar a la cartera de inversiones",