Improve validation and error handling in KnowledgeSpace API wrapper

[subh123321]

This PR improves robustness of the KnowledgeSpace API wrapper by adding:

• Input validation for user queries and IDs
• Consistent request timeouts
• Shared HTTP session for better performance
• Clearer error handling for network and timeout failures

These changes improve backend stability when running inside Docker
and make API failures easier to diagnose.

[QuantumByte-01]

Clean, well-scoped improvement — adds proper input validation, a typed exception hierarchy (ValueError, Timeout, RequestException), uses a requests.Session for connection pooling, and moves the timeout to a named constant. No unnecessary changes, good understanding of the codebase. Merging.