chore: gitignore .env (prevent secret leakage in public repo)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Security Level 5

.gitignore

@@ -1,3 +1,8 @@
 /target
 .cursor/
 __pycache__/
+
+# Local secrets / environment
+.env
+.env.*
+!.env.example