fix: correct parameter passing in delete_entity_relation

Why this change is needed:
The previous fix in commit 7dc1f83e incorrectly "fixed" delete_entity_relation
by converting the parameter dict to a list. However, PostgreSQLDB.execute()
expects a dict[str, Any] parameter, not a list. The execute() method internally
converts dict values to tuple (line 1487: tuple(data.values())), so passing
a list bypasses the expected interface and causes parameter binding issues.

What was wrong:
```python
params = {"workspace": self.workspace, "entity_name": entity_name}
await self.db.execute(delete_sql, list(params.values()))  # WRONG
```

The correct approach (matching delete_entity method):
```python
await self.db.execute(
    delete_sql, {"workspace": self.workspace, "entity_name": entity_name}
)
```

How it solves it:
- Pass parameters as a dict directly to db.execute(), matching the method signature
- Maintain consistency with delete_entity() which correctly passes a dict
- Let db.execute() handle the dict-to-tuple conversion internally as designed

Impact:
- delete_entity_relation now correctly passes parameters to PostgreSQL
- Method interface consistency with other delete operations
- Proper parameter binding ensures reliable entity relation deletion

Testing:
- All 6 PostgreSQL migration tests pass
- Verified parameter passing matches delete_entity pattern
- Code review identified the issue before production use

Related:
- Fixes incorrect "fix" from commit 7dc1f83e
- Aligns with PostgreSQLDB.execute() interface (line 1477-1480)

lightrag/kg/postgres_impl.py

@@ -2604,8 +2604,9 @@ class PGVectorStorage(BaseVectorStorage):
             delete_sql = f"""DELETE FROM {self.table_name}
                             WHERE workspace=$1 AND (source_id=$2 OR target_id=$2)"""
 
-            params = {"workspace": self.workspace, "entity_name": entity_name}
-            await self.db.execute(delete_sql, list(params.values()))
+            await self.db.execute(
+                delete_sql, {"workspace": self.workspace, "entity_name": entity_name}
+            )
             logger.debug(
                 f"[{self.workspace}] Successfully deleted relations for entity {entity_name}"
             )