Vinxi 0.5.7 + @solidjs/start 1.3.2 has a build bug where file-based API
routes (src/routes/api/*) are registered in the page router tree but never
mounted as Nitro handlers in the production build, so every /api/* request
returns a framework 404.
Fix: register a SolidStart middleware (src/middleware.ts) via the
middleware config field. The middleware intercepts all /api/* paths and
proxies them to the Rust gateway, bypassing the broken page router.
Covers:
- /api/gateway/* (catch-all proxy to gateway)
- /api/kb/categories
- /api/kb/articles
- /api/kb/articles/:slug
Also tightens the dev-server vite proxy from /api to /api/kb so it
doesn't shadow the new middleware in dev.
Removes the dead src/routes/api/ tree (no longer used).
