fix(providers): only block explicit official providers under proxy takeover

The proxy-takeover block previously fell back to the isOfficial heuristic
(empty base_url / missing key) when category was absent. That misjudged
custom providers whose endpoint lives in meta or whose fields are simply
unfilled: their switch button got disabled, making users think the config
was broken. That extra UI block was also "virtual" — the executor in
useProviderActions only ever honored category === "official", so the
front end blocked more than the backend would enforce.

Gate the block solely on explicit category === "official", matching the
executor and unifying both verdicts on a single source of truth.

Also rework the blocked-state UI:
- drop the red "blocked" badge for a plain disabled Enable button
- move title/cursor onto a wrapper span (disabled buttons set
  pointer-events:none, so an on-button title/cursor never fired)
- replace the account-ban warning tooltip with a lighter hint
  (provider.blockedByProxyHint), four locales kept in sync

src/i18n/locales/en.json

@@ -109,7 +109,7 @@
     "currentlyUsing": "Currently Using",
     "enable": "Enable",
     "inUse": "In Use",
-    "blockedByProxy": "Blocked",
+    "blockedByProxyHint": "Can't switch to an official provider while proxy takeover is active",
     "editProvider": "Edit Provider",
     "editProviderHint": "Configuration will be applied to the current provider immediately after update.",
     "deleteProvider": "Delete Provider",

src/i18n/locales/ja.json

@@ -109,7 +109,7 @@
     "currentlyUsing": "現在使用中",
     "enable": "有効化",
     "inUse": "使用中",
-    "blockedByProxy": "ブロック",
+    "blockedByProxyHint": "プロキシ引き継ぎモードでは公式プロバイダーに切り替えできません",
     "editProvider": "プロバイダーを編集",
     "editProviderHint": "保存すると現在のプロバイダーにすぐ反映されます。",
     "deleteProvider": "プロバイダーを削除",

src/i18n/locales/zh-TW.json

@@ -109,7 +109,7 @@
     "currentlyUsing": "目前使用",
     "enable": "啟用",
     "inUse": "使用中",
-    "blockedByProxy": "已攔截",
+    "blockedByProxyHint": "代理接管模式下無法切換至官方供應商",
     "editProvider": "編輯供應商",
     "editProviderHint": "更新設定後將立即套用至目前供應商。",
     "deleteProvider": "刪除供應商",

src/i18n/locales/zh.json

@@ -109,7 +109,7 @@
     "currentlyUsing": "当前使用",
     "enable": "启用",
     "inUse": "使用中",
-    "blockedByProxy": "已拦截",
+    "blockedByProxyHint": "代理接管模式下不可切换到官方供应商",
     "editProvider": "编辑供应商",
     "editProviderHint": "更新配置后将立即应用到当前供应商。",
     "deleteProvider": "删除供应商",