feat(send): migrate the Shield/Merge modal to the reference design

Presentation-only migration of ShieldDialog::render (Shield coinbase / Merge funds)
— a fund-moving modal:
- struct-form BeginOverlayDialog(OverlayDialogSpec{BlurFloat, cardWidth win.width,
  idSuffix shielddialog}) replacing the legacy positional overload
- drop the description divider and the form->footer divider (keep the post-submit
  operation-id section divider)
- 3 StyledButton -> TactileButton (submit / cancel / check-status)
- TR() the hardcoded "No shielded (z) address yet …" note -> new shield_no_zaddr_hint
  key, 8 langs (em-dash preserved); the "DRGX" ticker stays hardcoded per convention

The fund path is byte-for-byte unchanged: the can_submit guard, fee/utxo clamps, the
"ANY_TADDR" setup, the z_shieldcoinbase / z_mergetoaddress worker->post calls + their
opid/status/Notifications/trackOperation callbacks, and the BeginDisabled/tooltip logic.

Verified: build + ctest + hygiene clean; a 2-lens adversarial review
(fund-path-untouched / presentation-i18n) returned zero findings, proving the fund
path diffs byte-for-byte identical to HEAD via isolation diffs.

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

res/lang/de.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "Vorgang läuft...",
     "shield_max_utxos": "Max. UTXOs pro Vorgang",
     "shield_merge_done": "Abschirmung/Zusammenführung abgeschlossen!",
+    "shield_no_zaddr_hint": "Noch keine geschützte (z-)Adresse — erstellen Sie zuerst eine auf der Registerkarte Empfangen.",
     "shield_op_failed": "Vorgang fehlgeschlagen: ",
     "shield_op_submitted": "Vorgang übermittelt: ",
     "shield_operation_id": "Vorgangs-ID: %s",

res/lang/es.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "Operación en progreso...",
     "shield_max_utxos": "UTXOs máximos por operación",
     "shield_merge_done": "¡Protección/fusión completada!",
+    "shield_no_zaddr_hint": "Aún no hay dirección blindada (z) — crea una primero en la pestaña Recibir.",
     "shield_op_failed": "Operación fallida: ",
     "shield_op_submitted": "Operación enviada: ",
     "shield_operation_id": "ID de operación: %s",

res/lang/fr.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "Opération en cours...",
     "shield_max_utxos": "UTXOs max par opération",
     "shield_merge_done": "Blindage/fusion terminé !",
+    "shield_no_zaddr_hint": "Aucune adresse blindée (z) pour l'instant — créez-en une d'abord dans l'onglet Recevoir.",
     "shield_op_failed": "Échec de l'opération : ",
     "shield_op_submitted": "Opération soumise : ",
     "shield_operation_id": "ID d'opération : %s",

res/lang/ja.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "操作進行中...",
     "shield_max_utxos": "1回の操作あたりの最大UTXO数",
     "shield_merge_done": "シールド/統合が完了しました！",
+    "shield_no_zaddr_hint": "シールドアドレス（z）がまだありません — まず「受取」タブで作成してください。",
     "shield_op_failed": "操作に失敗しました: ",
     "shield_op_submitted": "操作を送信しました： ",
     "shield_operation_id": "オペレーション ID：%s",

res/lang/ko.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "작업 진행 중...",
     "shield_max_utxos": "작업당 최대 UTXO 수",
     "shield_merge_done": "차폐/통합이 완료되었습니다!",
+    "shield_no_zaddr_hint": "아직 보호된(z) 주소가 없습니다 — 먼저 받기 탭에서 만드세요.",
     "shield_op_failed": "작업 실패: ",
     "shield_op_submitted": "작업이 제출되었습니다: ",
     "shield_operation_id": "작업 ID: %s",

res/lang/pt.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "Operação em andamento...",
     "shield_max_utxos": "Máx. UTXOs por operação",
     "shield_merge_done": "Blindagem/fusão concluída!",
+    "shield_no_zaddr_hint": "Ainda não há endereço blindado (z) — crie um primeiro na aba Receber.",
     "shield_op_failed": "Falha na operação: ",
     "shield_op_submitted": "Operação enviada: ",
     "shield_operation_id": "ID da operação: %s",

res/lang/ru.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "Операция выполняется...",
     "shield_max_utxos": "Макс. UTXO за операцию",
     "shield_merge_done": "Экранирование/объединение завершено!",
+    "shield_no_zaddr_hint": "Пока нет защищённого (z-)адреса — сначала создайте его на вкладке «Получить».",
     "shield_op_failed": "Ошибка операции: ",
     "shield_op_submitted": "Операция отправлена: ",
     "shield_operation_id": "ID операции: %s",

res/lang/zh.json

@@ -1223,6 +1223,7 @@
     "shield_in_progress": "操作进行中...",
     "shield_max_utxos": "每次操作最大 UTXO 数",
     "shield_merge_done": "屏蔽/合并完成！",
+    "shield_no_zaddr_hint": "还没有屏蔽（z）地址 — 请先在“接收”标签页创建一个。",
     "shield_op_failed": "操作失败：",
     "shield_op_submitted": "操作已提交：",
     "shield_operation_id": "操作 ID：%s",