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-core/src/edge.rs

@@ -51,8 +51,8 @@ pub struct Edge {
     pub project_id: String,
     
     // Relationship
-    pub source_entity_id: String,  // FK to knowledge_node
-    pub target_entity_id: String,  // FK to knowledge_node
+    pub source_entity_id: String,  // FK to memory_entity
+    pub target_entity_id: String,  // FK to memory_entity
     pub relation_type: String,
     pub fact: String,
     pub fact_embedding: Option<Vec<f32>>,
@@ -71,7 +71,7 @@ pub struct Edge {
     
     // Provenance
     pub source_episode_id: Option<i64>,  // FK to memory_node
-    pub invalidated_by: Option<String>,  // FK to knowledge_edge.id
+    pub invalidated_by: Option<String>,  // FK to memory_edge.id
     
     // Contradiction handling
     pub contradiction_status: ContradictionStatus,