feat(settings): rename to "Import Private Key" + add scan height to it

Follow-up to the key/viewing-key button split:

- Rename the "Import Key…" button to "Import Private Key…" (settings_import_key
  value in en + all 8 langs, reusing the existing import_key_title wording) so it
  reads as the natural counterpart to "Import Viewing Key…". The dialog title was
  already "Import Private Key". The viewing-key wrong-type redirect hint now names
  the renamed button.

- Show the "scan from block height" field in the private-key (spending) dialog too,
  not just the viewing-key one. z_importkey accepts a start height, so a shielded
  spend import of a recent key needn't rescan the whole chain. Transparent WIF
  (importprivkey) has no such param, so once a transparent key is recognized the
  field is disabled, its buffer cleared, and a "Transparent keys always rescan
  fully" note replaces the hint. importPrivateKey already gates the start-height
  append on (viewing || shielded), so transparent imports never receive it.

- i18n: shared scan keys renamed import_viewkey_scan_{label,hint} ->
  import_scan_{label,hint}; added import_scan_transparent (en + 8 langs).

Reviewed via an adversarial multi-agent pass (rpc-routing / i18n / ui-logic /
consistency); only two nits surfaced (stale disabled-field value + a stale
comment), both fixed here.

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

res/lang/ja.json

@@ -444,12 +444,13 @@
     "import_key_wrong_type": "これは閲覧鍵のようです。代わりに「閲覧鍵をインポート」を使用してください。",
     "import_key_z_format": "Zアドレス支出鍵 (secret-extended-key-...)",
     "import_private_key": "秘密鍵をインポート...",
+    "import_scan_hint": "0 = 最初から再スキャン",
+    "import_scan_label": "スキャン開始ブロック高（任意）",
+    "import_scan_transparent": "透明鍵は常に全体を再スキャンします",
     "import_viewkey_field": "閲覧鍵",
     "import_viewkey_note": "監視のみ：閲覧鍵はアドレスの残高と取引を表示できますが、資金を送金することはできません。",
-    "import_viewkey_scan_hint": "0 = 最初から再スキャン",
-    "import_viewkey_scan_label": "スキャン開始ブロック高（任意）",
     "import_viewkey_title": "閲覧鍵をインポート",
-    "import_viewkey_wrong_type": "これは支払い鍵のようです。代わりに「鍵をインポート」を使用してください。",
+    "import_viewkey_wrong_type": "これは支払い鍵のようです。代わりに「秘密鍵をインポート」を使用してください。",
     "incorrect_passphrase": "パスフレーズが正しくありません",
     "incorrect_pin": "PINが正しくありません",
     "insufficient_funds": "この金額と手数料に対して残高が不足しています。",
@@ -1111,7 +1112,7 @@
     "settings_gradient_bg": "グラデーション背景",
     "settings_gradient_desc": "テクスチャ背景を滑らかなグラデーションに置換",
     "settings_idle_after": "経過後",
-    "settings_import_key": "鍵をインポート...",
+    "settings_import_key": "秘密鍵をインポート...",
     "settings_import_viewkey": "閲覧鍵をインポート...",
     "settings_language_note": "注意：一部のテキストは更新に再起動が必要です",
     "settings_lock_now": "今すぐロック",