feat(config): integrate rate limiting and CORS configuration from furt.conf

- Add RateLimiter:configure() function to accept config-based limits
- Integrate security section parameters (rate_limit_api_key_max, ip_max, window)
- Add CORS configuration from config file with environment fallback
- Replace hardcoded rate limiting defaults with configurable values
- Add test endpoint control via config.security.enable_test_endpoint
- Update startup logging to show actual configured rate limits
- Add configuration validation and detailed startup information

Rate limiting now uses values from [security] section instead of hardcoded
defaults. CORS origins prioritize config file over environment variables.

Related to DAW/furt#89

config/furt.conf.example

@@ -4,8 +4,20 @@
 # Server configuration
 [server]
 host = 127.0.0.1
-port = 8080
+port = 7811
 log_level = info
+log_requests = true
+client_timeout = 10
+
+# CORS configuration
+cors_allowed_origins = http://localhost:1313,http://127.0.0.1:1313,https://dragons-at-work.de,https://www.dragons-at-work.de
+
+# Security settings
+[security]
+rate_limit_api_key_max = 60
+rate_limit_ip_max = 100
+rate_limit_window = 3600
+enable_test_endpoint = false
 
 # Default SMTP settings (used when API keys don't have custom SMTP)
 [smtp_default]