revert: restore memory_entity/memory_edge table names

knowledge_* namespace reserved for future agentic learning tables.
memory_* namespace used for facts, events, and entity graph.

- knowledge_node → memory_entity (reverted)
- knowledge_edge → memory_edge (reverted)
- Old provenance DAG (child_sha/parent_sha) renamed to
  memory_edge_provenance via migration 009
- Kept: runtime queries in versioning.rs, UUID casts, init_schema additions

crates/mem-store/migrations/006_phase4_community_detection.sql

@@ -47,7 +47,7 @@ CREATE TABLE IF NOT EXISTS community_member_map (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
     project_id VARCHAR(255) NOT NULL,
     community_id UUID NOT NULL REFERENCES memory_community(id) ON DELETE CASCADE,
-    entity_id UUID NOT NULL REFERENCES knowledge_node(id) ON DELETE CASCADE,
+    entity_id UUID NOT NULL REFERENCES memory_entity(id) ON DELETE CASCADE,
     label_propagation_run_id UUID REFERENCES label_propagation_run(id) ON DELETE SET NULL,
     
     -- Label strength (0-1, higher = stronger membership)