✨ feat(ratio-sync, ui): add built‑in “Official Ratio Preset” and harden upstream sync

Backend (controller/ratio_sync.go):
- Add built‑in official upstream to GetSyncableChannels (ID: -100, BaseURL: https://basellm.github.io)
- Support absolute endpoint URLs; otherwise join BaseURL + endpoint (defaults to /api/ratio_config)
- Harden HTTP client:
  - IPv4‑first with IPv6 fallback for github.io
  - Add ResponseHeaderTimeout
  - 3 attempts with exponential backoff (200/400/800ms)
- Validate Content-Type and limit response body to 10MB (safe decode via io.LimitReader)
- Robust parsing: support type1 ratio_config map and type2 pricing list
- Use net.SplitHostPort for host parsing
- Use float tolerance in differences comparison to avoid false mismatches
- Remove unused code (tryDirect) and improve warnings

Frontend:
- UpstreamRatioSync.jsx: auto-assign official endpoint to /llm-metadata/api/newapi/ratio_config-v1-base.json
- ChannelSelectorModal.jsx:
  - Pin the official source at the top of the list
  - Show a green “官方” tag next to the status
  - Refactor status renderer to accept the full record

Notes:
- Backward compatible; no API surface changes
- Official ratio_config reference: https://basellm.github.io/llm-metadata/api/newapi/ratio_config-v1-base.json

web/src/hooks/common/useHeaderBar.js

@@ -64,7 +64,7 @@ export const useHeaderBar = ({ onMobileMenuToggle, drawerOpen }) => {
         if (typeof modules.pricing === 'boolean') {
           modules.pricing = {
             enabled: modules.pricing,
-            requireAuth: false  // 默认不需要登录鉴权
+            requireAuth: false, // 默认不需要登录鉴权
           };
         }