fix: expand .gitignore to cover all .env.* variants

Replaced narrow .env.local / .env.*.local rules with .env.* to prevent
accidental commit of .env.production, .env.development, .env.staging, etc.
Explicitly allowlisted .env.example so it remains tracked.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -19,8 +19,8 @@ logs/
 
 # Environment files
 .env
-.env.local
-.env.*.local
+.env.*
+!.env.example
 
 # Node / JavaScript
 node_modules/