✨ 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/components/layout/HeaderBar/Navigation.jsx

@@ -21,7 +21,13 @@ import React from 'react';
 import { Link } from 'react-router-dom';
 import SkeletonWrapper from './SkeletonWrapper';
 
-const Navigation = ({ mainNavLinks, isMobile, isLoading, userState, pricingRequireAuth }) => {
+const Navigation = ({
+  mainNavLinks,
+  isMobile,
+  isLoading,
+  userState,
+  pricingRequireAuth,
+}) => {
   const renderNavLinks = () => {
     const baseClasses =
       'flex-shrink-0 flex items-center gap-1 font-semibold rounded-md transition-all duration-200 ease-in-out';