website: generate the API reference from source (cordis + all 15 harness services)

scripts/gen-website-api.ts renders website/zh-CN/api/{cordis,harness}/* and the
api-sidebar.json fragment the VitePress config imports, so pages and navigation
can never drift from the code: signatures, @param/@returns prose, dispatch
modes, and GitHub source links are extracted, never transcribed, and the
generator hard-errors on any rendered member missing docs. verify-website-api
(doc-sync + run-gates) is the freshness gate.

Replaces the hand-written zh api pages (7 pages covering 7 of 15 services,
with phantom APIs: Context.current/Context.events, agent/post-step, tool/call,
compact/*, llm/pre-request none of which exist) with generated English
references: 5 cordis pages, 15 per-service pages, and a 35-event catalog
grouped by scope. The hand-written hub api/index.md stays and now indexes the
full surface; zh for these pages arrives with the unified translation flow.

scripts/run-gates.ts

@@ -264,6 +264,7 @@ function docSyncLeafGates(): Gate[] {
     pnpmScript('config-catalog', 'verify-config-catalog', { label: 'config catalog' }),
     pnpmScript('persistence-catalog', 'verify-persistence-catalog', { label: 'persistence catalog' }),
     pnpmScript('doc-graphs', 'verify-doc-graphs', { label: 'doc graphs' }),
+    pnpmScript('website-api', 'verify-website-api', { label: 'website api' }),
     pnpmScript('markdown-wrap', 'verify-md-wrap', { label: 'markdown wrap' }),
     pnpmScript('markdown-links', 'verify-md-links', { label: 'markdown links' }),
     pnpmScript('doc-refs', 'verify-doc-refs', { label: 'doc refs' }),