Implement Proxy support for AI Assistant in network setups enforcing Proxy usage

**Is your feature request related to a problem? Please describe.**
When connected to a corporate network via VPN that enforces proxy usage for external access, the AI Assistant is currently non-functional. All queries fail with a connection error (please see the attached stack trace).

**Describe the solution you'd like**
The AI Assistant should be able to communicate with the LLM even when connected via a corporate VPN that requires a proxy for all outbound traffic to external IP addresses.

**Describe alternatives you've considered**
I am not aware of any alternatives.

**Additional context**
From a user perspective, I prefer a solution that:

Is managed via a single configuration point.

Is unified for all outbound network communication initiated by DBeaver, including downloading DB drivers, checking for version updates, AI Assistant communication, and any other tools requiring Internet access.

[2025-12-13_dbeaver_AI_agent_connection_problem.txt](https://github.com/user-attachments/files/24140167/2025-12-13_dbeaver_AI_agent_connection_problem.txt)