Create a method that provides weather-based recommendations for cities by integrating with OpenWeatherMap APIs. Your solution will demonstrate advanced integration patterns by chaining multiple API calls and handling complex data transformations.

Your method should:

1. Validate input (return "Invalid city name" for null/empty)
2. Call geocoding API to get coordinates
3. Call weather API to get current conditions
4. Convert temperature from Kelvin to Celsius
5. Return temperature-based recommendation:

   • 25°C: "Hot"

   • 15-25°C: "Warm"
   • 5-15°C: "Cool"
   • <= 5°C: "Cold"

Handle all API errors gracefully by returning appropriate error messages.