Implement agent version tracking to diagnose deployment issues:
- Add get_agent_hash() method to extract Nix store hash from executable path
- Collect system_agent_hash metric in NixOS collector
- Display "Agent Hash" in system panel under NixOS section
- Update metric filtering to include agent hash
This helps identify which version of the agent is actually running
when troubleshooting deployment or metric collection issues.
Christoffer Martinsson
c5ec529210