Add fleet.inventory and fleet.path_contracts to config.yaml:
- Central source of truth for IPs, ports, roles, remote paths
- Introduce get_config_path(), load_fleet_inventory(), get_path_contract()
- Updated fleet_llama.py, self_healing.py, telemetry.py, agent_dispatch.py,
skill_installer.py to read from config instead of hard-coded dicts/paths
- Documented inventory contract and override mechanism in scripts/README.md
Scripts retain forward-compatible fallback defaults for backwards compatibility.
Closes#433
