🎨 refactor(ui): redesign channel extra settings section in EditChannelModal

- Extract channel extra settings into a dedicated Card component for better visual hierarchy
- Replace custom gray background container with consistent Form component styling
- Simplify layout structure by removing complex Row/Col grid layout in favor of native Form component layout
- Unify help text styling by using extraText prop consistently across all form fields
- Move "Settings Documentation" link to card header subtitle for better accessibility
- Improve visual consistency with other setting cards by using matching design patterns

The channel extra settings (force format, thinking content conversion, pass-through body, proxy address, and system prompt) now follow the same design language as other configuration sections, providing a more cohesive user experience.

Affected settings:
- Force Format (OpenAI channels only)
- Thinking Content Conversion
- Pass-through Body
- Proxy Address
- System Prompt

web/src/i18n/locales/en.json

@@ -1331,8 +1331,7 @@
   "对于官方渠道，new-api已经内置地址，除非是第三方代理站点或者Azure的特殊接入地址，否则不需要填写": "For official channels, the new-api has a built-in address. Unless it is a third-party proxy site or a special Azure access address, there is no need to fill it in",
   "渠道额外设置": "Channel extra settings",
   "强制格式化": "Force format",
-  "强制格式化（只适用于OpenAI渠道类型）": "Force format (Only for OpenAI channel types)",
-  "强制将响应格式化为 OpenAI 标准格式": "Force format responses to OpenAI standard format",
+  "强制将响应格式化为 OpenAI 标准格式（只适用于OpenAI渠道类型）": "Force format responses to OpenAI standard format (Only for OpenAI channel types)",
   "思考内容转换": "Thinking content conversion",
   "将 reasoning_content 转换为 <think> 标签拼接到内容中": "Convert reasoning_content to <think> tags and append to content",
   "透传请求体": "Pass through body",