fix: move hardcoded admin credentials to env vars and fix console.log syntax error

[bennytimz]

This PR fixes two related issues in lib/supabase/initialize-admin-user.ts:

1. Hardcoded admin credentials
   The admin password (123456) was hardcoded directly in source code. Anyone with
   read access to the repository knows the default admin password. If a developer
   deploys this app without changing the password, the admin account is immediately
   compromised.
   Fix: The password is now read from a new ADMIN_PASSWORD environment variable.
   The app logs a clear error and skips admin creation if the variable is not set,
   rather than silently creating an account with a publicly known password.
   The email already had an ADMIN_EMAIL env var in .env.example but the code
   wasn't using it — that is also fixed here.
2. Syntax error in console.log
   // Before (crashes at runtime — missing opening parenthesis)
   console.logAdmin user with email ${adminEmail} created successfully.);

// After (correct)
console.log(Admin user with email ${adminEmail} created successfully.);

This would cause an uncaught SyntaxError the first time the admin user is
successfully created, crashing the initialization function.

Files changed

• lib/supabase/initialize-admin-user.ts — read credentials from env vars, fix syntax error
• .env.example — add ADMIN_PASSWORD variable
• README.md — update admin account documentation