refactor: rename memory_entity→knowledge_node, knowledge graph edge→knowledge_edge

Resolves table name collision between:
- memory_edge (provenance DAG: child_sha/parent_sha) — KEPT
- knowledge_edge (knowledge graph: source_id/target_id) — NEW NAME

Changes:
- memory_entity → knowledge_node (all .rs + migrations 003-009)
- knowledge graph memory_edge → knowledge_edge
- memory_entity_version → knowledge_node_version
- memory_edge_version → knowledge_edge_version
- Added knowledge_node + knowledge_edge to init_schema()
- Converted versioning.rs from sqlx::query_as! to runtime queries
  (avoids stale sqlx offline cache dependency)
- Fixed UUID cast: $1::UUID for String→UUID column binds
- Fixed column names: source_entity_id→source_id, target_entity_id→target_id

Production DB: knowledge_node + knowledge_edge tables created,
memory_entity VIEW points to knowledge_node for backward compat.

crates/mem-store/migrations/007_versioning_schema.sql

@@ -5,7 +5,7 @@
 BEGIN;
 
 -- Entity version snapshots (immutable)
-CREATE TABLE IF NOT EXISTS memory_entity_version (
+CREATE TABLE IF NOT EXISTS knowledge_node_version (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
     entity_id VARCHAR(255) NOT NULL,
     version_num INTEGER NOT NULL,
@@ -28,7 +28,7 @@ CREATE TABLE IF NOT EXISTS memory_entity_version (
 );
 
 -- Edge version snapshots
-CREATE TABLE IF NOT EXISTS memory_edge_version (
+CREATE TABLE IF NOT EXISTS knowledge_edge_version (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
     edge_id UUID NOT NULL,
     version_num INTEGER NOT NULL,
@@ -52,22 +52,22 @@ CREATE TABLE IF NOT EXISTS memory_edge_version (
 
 -- Indexes for efficient lookups
 CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_entity_version_entity_id 
-    ON memory_entity_version(entity_id, version_num DESC);
+    ON knowledge_node_version(entity_id, version_num DESC);
 
 CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_entity_version_changed_at 
-    ON memory_entity_version(changed_at DESC);
+    ON knowledge_node_version(changed_at DESC);
 
 CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_entity_version_changed_by 
-    ON memory_entity_version(changed_by);
+    ON knowledge_node_version(changed_by);
 
 CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_edge_version_edge_id 
-    ON memory_edge_version(edge_id, version_num DESC);
+    ON knowledge_edge_version(edge_id, version_num DESC);
 
 CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_edge_version_changed_at 
-    ON memory_edge_version(changed_at DESC);
+    ON knowledge_edge_version(changed_at DESC);
 
 CREATE INDEX CONCURRENTLY IF NOT EXISTS idx_edge_version_changed_by 
-    ON memory_edge_version(changed_by);
+    ON knowledge_edge_version(changed_by);
 
 -- Immutability enforcement: version tables are append-only
 CREATE OR REPLACE FUNCTION prevent_version_table_modification()
@@ -77,19 +77,19 @@ BEGIN
 END;
 $$ LANGUAGE plpgsql;
 
-CREATE TRIGGER memory_entity_version_immutable
-    BEFORE UPDATE OR DELETE ON memory_entity_version
+CREATE TRIGGER knowledge_node_version_immutable
+    BEFORE UPDATE OR DELETE ON knowledge_node_version
     FOR EACH ROW EXECUTE FUNCTION prevent_version_table_modification();
 
-CREATE TRIGGER memory_edge_version_immutable
-    BEFORE UPDATE OR DELETE ON memory_edge_version
+CREATE TRIGGER knowledge_edge_version_immutable
+    BEFORE UPDATE OR DELETE ON knowledge_edge_version
     FOR EACH ROW EXECUTE FUNCTION prevent_version_table_modification();
 
 COMMIT;
 
 -- Rollback (for reference):
--- DROP TRIGGER memory_entity_version_immutable ON memory_entity_version;
--- DROP TRIGGER memory_edge_version_immutable ON memory_edge_version;
+-- DROP TRIGGER knowledge_node_version_immutable ON knowledge_node_version;
+-- DROP TRIGGER knowledge_edge_version_immutable ON knowledge_edge_version;
 -- DROP FUNCTION prevent_version_table_modification();
--- DROP TABLE memory_entity_version;
--- DROP TABLE memory_edge_version;
+-- DROP TABLE knowledge_node_version;
+-- DROP TABLE knowledge_edge_version;