Ship agent evidence and runtime polish

[BadgerOps]

Summary

• add entity_evidence storage and confidence-aware host identity selection for agent ingest
• expose host evidence in APIs and the Host Detail evidence panel
• polish passive agent runtime: 15s polling, service restart behavior, API-key recovery, local network noise filtering, and startup version logging

Closes #79

Tests

• nix develop -c .venv/bin/python -m pytest agent/tests/test_grapheon_agent.py -q
• nix develop -c .venv/bin/python -m pytest