fix(proxy-ui): accept IPv6 listen addresses in ProxyPanel validation

The backend already understands `::` -> `::1` and wraps IPv6 literals
in brackets (services/proxy.rs), but the panel's save-time validator
only accepted localhost, 0.0.0.0, and IPv4 dotted-quads. Users who
wanted to listen on an IPv6 loopback had to bypass the UI and edit
config directly.

Add an isValidIpv6 helper that requires at least one ':' and round-trips
through `new URL('http://[<addr>]/')` so the platform's built-in IPv6
parser does the heavy lifting (covers compressed `::`, full 8-group
form, zone IDs). Update the invalidAddress copy in zh / en / ja so the
error message reflects the new accepted set.

src/i18n/locales/en.json

@@ -2196,7 +2196,7 @@
         "saveFailed": "Save failed: {{error}}"
       },
       "invalidPort": "Invalid port, please enter a number between 1024-65535",
-      "invalidAddress": "Invalid address, please enter a valid IP address (e.g. 127.0.0.1) or localhost",
+      "invalidAddress": "Invalid address. Enter an IPv4 (e.g. 127.0.0.1), IPv6 (e.g. ::1), or localhost",
       "configSaved": "Routing configuration saved",
       "configSaveFailed": "Failed to save configuration",
       "restartRequired": "Restart routing service for address or port changes to take effect"

src/i18n/locales/ja.json

@@ -2196,7 +2196,7 @@
         "saveFailed": "保存に失敗しました: {{error}}"
       },
       "invalidPort": "無効なポートです。1024〜65535 の数値を入力してください",
-      "invalidAddress": "無効なアドレスです。有効な IP アドレス（例: 127.0.0.1）または localhost を入力してください",
+      "invalidAddress": "無効なアドレスです。IPv4（例: 127.0.0.1）、IPv6（例: ::1）、または localhost を入力してください",
       "configSaved": "ルーティング設定を保存しました",
       "configSaveFailed": "設定の保存に失敗しました",
       "restartRequired": "アドレスまたはポートの変更を反映するにはルーティングサービスの再起動が必要です"

src/i18n/locales/zh.json

@@ -2196,7 +2196,7 @@
         "saveFailed": "保存失败: {{error}}"
       },
       "invalidPort": "端口无效，请输入 1024-65535 之间的数字",
-      "invalidAddress": "地址无效，请输入有效的 IP 地址（如 127.0.0.1）或 localhost",
+      "invalidAddress": "地址无效，请输入 IPv4（如 127.0.0.1）、IPv6（如 ::1）或 localhost",
       "configSaved": "路由配置已保存",
       "configSaveFailed": "保存配置失败",
       "restartRequired": "修改地址或端口后需要重启路由服务才能生效"