refactor: API reference lives at api.interscript.org/docs

[ronaldtse]

Summary

• deployed API content belongs to api.interscript.org: the site's interactive api-docs page is replaced by a redirect page to https://api.interscript.org/docs (served by the worker itself since api-worker 1.0.2)
• primary nav "API reference" now links directly to the API's own docs
• tests updated: redirect assertion replaces the interactive-reference assertions; nav destination lists point at the external URL

Test plan

• 255/255 vitest, check 0 errors, lint, format
• build emits /api-docs/index.html with the redirect