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.

.sqlx/query-c045466e1fe037dbdafea1008f262f4e48f104ea77732aa1d32ecb797f70e71d.json

@@ -1,6 +1,6 @@
 {
   "db_name": "PostgreSQL",
-  "query": "\n            SELECT \n                version_num,\n                operation,\n                snapshot,\n                changed_at,\n                changed_by,\n                COALESCE(fields_changed, '{}') as \"fields_changed!\"\n            FROM memory_entity_version\n            WHERE entity_id = $1 AND version_num = $2\n            ",
+  "query": "\n            SELECT \n                version_num,\n                operation,\n                snapshot,\n                changed_at,\n                changed_by,\n                COALESCE(fields_changed, '{}') as \"fields_changed!\"\n            FROM knowledge_node_version\n            WHERE entity_id = $1 AND version_num = $2\n            ",
   "describe": {
     "columns": [
       {