fix: PEM newline parsing + shared config extra=ignore

- Add field_validator to expand literal \n in PEM keys (auth config + shared config)
- Set extra='ignore' on shared Settings so service-specific .env vars don't cause ValidationError
- Add *.pem to .gitignore

.gitignore

@@ -13,6 +13,9 @@ env/
 # Environment variables
 .env
 
+# Cryptographic keys
+*.pem
+
 # IDE
 .vscode/
 .idea/