Implement version compatibility matrix for agent registry

[kivo360]

Problem

The agent registry (backend/omoi_os/services/agent_registry.py) has two incomplete TODOs:

• Line ~465: TODO: Implement actual version compatibility matrix
• Line ~489: TODO: Implement actual resource availability check

Without these, agents can be assigned tasks they're not compatible with, and resource limits aren't enforced.

What to do

1. Define a version compatibility matrix (which agent versions can handle which task types)
2. Check resource availability before assigning tasks (memory, CPU, sandbox slots)
3. Reject task assignments that would exceed resource limits

Difficulty: Medium | Skill: Python (backend services)