feat(api-docs): split the API docs page into tabs

The page stacked the WebSocket event cards above every Panel API operation
in one long scroll. The WebSocket events and the 3X-UI Panel API now sit in
separate tabs, and the Panel API shows one OpenAPI tag at a time through
section tabs placed between the Authorize bar and the operations.

The section tabs replace Swagger UI's FilterContainer and wrap the
taggedOperations selector, so all sections share one Swagger instance and
keep authorization and try-it-out state. Swagger's own filter matches tags
by substring ("Settings" would also show "Xray Settings") and does nothing
until set, so the wrapper matches the exact tag and defaults to the first.
Tag names come from the loaded spec rather than importing endpoints.ts,
which would have grown the page chunk from 23 kB to 119 kB.

frontend/src/pages/api-docs/ApiDocsPage.css

@@ -45,15 +45,14 @@
 }
 
 .api-docs-page .websocket-events {
-  margin-bottom: 16px;
   padding: 20px;
   background: var(--bg-card);
   border: 1px solid var(--ant-color-border-secondary);
   border-radius: 8px;
 }
 
-.api-docs-page .websocket-events h2 {
-  margin-top: 0;
+.api-docs-page .swagger-ui .section-tabs {
+  margin-top: 20px;
 }
 
 .api-docs-page .websocket-events pre {