Tag /api/gateway requests with direct-gateway feature header

[emilieschario]

Summary

• Requests hitting /api/gateway/ now have x-kilocode-feature: direct-gateway injected before being forwarded to the openrouter handler
• Any client-supplied x-kilocode-feature header is overwritten
• Added tests covering both behaviours

[kiloconnect]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Clean change that wraps the gateway route handler to inject the x-kilocode-feature: direct-gateway header before forwarding to the openrouter POST handler. The server-side header injection correctly prevents client spoofing, 'direct-gateway' is a valid FEATURE_VALUES entry, and the NextRequest constructor properly clones the body from the original request. Tests cover both the default case and the overwrite case.

Files Reviewed (2 files)

• src/app/api/gateway/[...path]/route.ts
• src/app/api/gateway/[...path]/route.test.ts