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.

AGENTS.md

@@ -30,7 +30,7 @@ packages/    Harness packages at packages/<group>/<pkg>/, all named @deepseek-ai
 examples/    Runnable demos: thin cordis.yml leaves over the app packages (see examples/AGENTS.md)
 docs/        architecture, generated catalogs, RFCs, postmortems, cookbook (see docs/AGENTS.md)
 scripts/     repo gates and generators
-website/     VitePress docs site (zh-CN)
+website/     VitePress docs site (zh-CN); api/ pages generated from source
 ```
 
 Per-package map: the group READMEs, indexed from [packages/README.md](packages/README.md).