sql first refactor

backend/app/db_json.py

@@ -1,7 +1,8 @@
-"""asyncpg Record → JSON-serializovatelný dict."""
+"""asyncpg Record → JSON-serializovatelný dict + helper pro jsonb z fn_*."""
 
 from __future__ import annotations
 
+import json
 from datetime import date, datetime, timezone
 from decimal import Decimal
 from typing import Any
@@ -33,3 +34,17 @@ def record_to_dict(r: asyncpg.Record) -> dict[str, Any]:
         else:
             out[k] = str(v)
     return out
+
+
+async def fetch_json(conn: asyncpg.Connection, query: str, *args: Any) -> Any:
+    """fetchval pro dotazy vracející jsonb (např. select ems.fn_*(...))."""
+    v = await conn.fetchval(query, *args)
+    if v is None:
+        return None
+    if isinstance(v, (dict, list)):
+        return v
+    if isinstance(v, (bytes, memoryview)):
+        return json.loads(bytes(v).decode("utf-8"))
+    if isinstance(v, str):
+        return json.loads(v)
+    return v