✨ 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/table/channels/ChannelsColumnDefs.jsx

@@ -231,11 +231,14 @@ export const getChannelsColumns = ({
                     theme='outline'
                     onClick={(e) => {
                       e.stopPropagation();
-                      navigator.clipboard.writeText(record.remark).then(() => {
-                        showSuccess(t('复制成功'));
-                      }).catch(() => {
-                        showError(t('复制失败'));
-                      });
+                      navigator.clipboard
+                        .writeText(record.remark)
+                        .then(() => {
+                          showSuccess(t('复制成功'));
+                        })
+                        .catch(() => {
+                          showError(t('复制失败'));
+                        });
                     }}
                   >
                     {t('复制')}