security: remove .env from git tracking and add to .gitignore

BREAKING CHANGE: .env file is no longer tracked in git for security.
Each environment must maintain its own .env file with secrets.
Use .env.example as a template.

.gitignore

@@ -23,6 +23,7 @@ yarn-debug.log*
 yarn-error.log*
 
 # Local env files
+.env
 .env*.local
 
 # Vercel