Fix foreign key constraint error when creating proxy hosts

The issue occurred because the auth system uses a hardcoded JWT user ID (1)
that didn't exist in the database, causing foreign key constraint violations
when creating proxy hosts.

Changes:
- Added init-db.ts to ensure admin user exists in database
- Added instrumentation.ts to run DB initialization on server startup
- Admin user (from ADMIN_USERNAME env var) is now created with ID 1
- Matches the hardcoded ID in auth.ts for JWT tokens

Fixes foreign key constraint error (P2003) when creating proxy hosts.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
+import "./.next/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.