security: add comprehensive secret/credential patterns to .gitignore

- Block environment files: *.env, .env*, *.env.*
- Block certificates: *.pem, *.key, *.crt, *.cer, *.der
- Block encrypted files: *.gpg, *.p12, *.pfx
- Block SSH keys: *_rsa, *_dsa, *_ecdsa, *id_ed25519*, id_rsa*, id_dsa*
- Block credentials: credentials*, secrets*, .npmrc, .pypirc

Author: nickotmazgin

.gitignore

@@ -69,3 +69,27 @@ GITHUB_SETUP_COMPLETE.md
 
 # System scripts (not extension-related)
 tools/system_security_hardening.sh
+
+# Security: Never commit secrets or credentials
+*.env
+*.env.*
+.env*
+*.pem
+*.key
+*.gpg
+*.p12
+*.pfx
+*_rsa
+*_dsa
+*_ecdsa
+*id_ed25519*
+id_rsa*
+id_dsa*
+id_ecdsa*
+credentials*
+secrets*
+.npmrc
+.pypirc
+*.crt
+*.cer
+*.der