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/zh.json

@@ -444,12 +444,13 @@
     "import_key_wrong_type": "这看起来像查看密钥。请改用\"导入查看密钥\"。",
     "import_key_z_format": "Z 地址花费密钥 (secret-extended-key-...)",
     "import_private_key": "导入私钥...",
+    "import_scan_hint": "0 = 从头重新扫描",
+    "import_scan_label": "从区块高度开始扫描（可选）",
+    "import_scan_transparent": "透明密钥始终完整重新扫描",
     "import_viewkey_field": "查看密钥",
     "import_viewkey_note": "仅查看：查看密钥可显示地址的余额和交易，但无法花费其资金。",
-    "import_viewkey_scan_hint": "0 = 从头重新扫描",
-    "import_viewkey_scan_label": "从区块高度开始扫描（可选）",
     "import_viewkey_title": "导入查看密钥",
-    "import_viewkey_wrong_type": "这看起来像花费密钥。请改用\"导入密钥\"。",
+    "import_viewkey_wrong_type": "这看起来像花费密钥。请改用\"导入私钥\"。",
     "incorrect_passphrase": "密码错误",
     "incorrect_pin": "PIN 错误",
     "insufficient_funds": "余额不足以支付此金额加手续费。",
@@ -1111,7 +1112,7 @@
     "settings_gradient_bg": "渐变背景",
     "settings_gradient_desc": "用平滑渐变替换纹理背景",
     "settings_idle_after": "之后",
-    "settings_import_key": "导入密钥...",
+    "settings_import_key": "导入私钥...",
     "settings_import_viewkey": "导入查看密钥...",
     "settings_language_note": "注意：部分文本需要重启才能更新",
     "settings_lock_now": "立即锁定",