Implement SAND-WP-0008: host telemetry and self-canary

Add profile.sandbox-canary, HostSnapshot/inventory/stale schemas, SSH
collectors, before/after provision deltas, telemetry export to State Hub
and local JSON, default `sandboxer create` self-deploy, inspect/reap-stale
CLI, runbook, and CoulombCore verification (26 tests pass).

tests/test_defaults.py

@@ -0,0 +1,12 @@
+"""Default profile resolution."""
+
+from sandboxer.defaults import DEFAULT_CANARY_PROFILE, DEFAULT_COMPOSE_PROFILE, repo_root
+
+
+def test_repo_root_points_at_sand_boxer() -> None:
+    assert repo_root().name == "sand-boxer"
+
+
+def test_canary_profile_constant() -> None:
+    assert DEFAULT_CANARY_PROFILE == "profile.sandbox-canary"
+    assert DEFAULT_COMPOSE_PROFILE == "profile.compose-e2e"