feat(PMEM-WP-0017): federated store management CLI and activity reports

Add phase_memory.management for cross-store discovery and windowed
activity reporting. Extend the phase-memory CLI with stores list and
report commands, plus make report-7d for the default weekly operator view.

tests/fixtures/management/registry.json

@@ -0,0 +1,13 @@
+{
+  "schema_version": "phase_memory.management.store_registry.v1",
+  "stores": [
+    {
+      "store_id": "fixture-local-graph",
+      "path": "local-store",
+      "store_kind": "local_graph",
+      "profile_id": "local-dev",
+      "label": "Fixture local graph store",
+      "registered_at": "2026-07-01T10:00:00+00:00"
+    }
+  ]
+}