feat: add configurable test mode and rate limiting

- Add TestMode, RateLimitEnabled, RequestsPerMinute to Config
- Add getEnvBool() and getEnvInt() helper functions
- Update rate limiter to support enabled/disabled state
- Pass test environment variables through docker-compose
- Configure rate limiter dynamically in main.go

This allows disabling rate limiting for integration testing while
maintaining security in production environments.

cmd/server/main.go

@@ -67,7 +67,12 @@ func main() {
 	e.Use(ratelimit.RequestTracingMiddleware(cfg))
 
 	// Rate limiter for auth endpoints
-	rateLimiter := ratelimit.NewRateLimiter(ratelimit.DefaultRateLimiterConfig())
+	rateLimiterConfig := ratelimit.RateLimiterConfig{
+		Enabled:           cfg.RateLimitEnabled,
+		RequestsPerMinute: cfg.RequestsPerMinute,
+		CleanupInterval:   5 * time.Minute,
+	}
+	rateLimiter := ratelimit.NewRateLimiter(rateLimiterConfig)
 	rateLimitMiddleware := ratelimit.RateLimiterMiddleware(rateLimiter)
 
 	// Auth routes (no auth required, but rate limited)