fix: wrap abilities dict with Json() for JSONB insert (#13)

Problem: Creating new training types via Admin UI resulted in
'Internal Server Error' because abilities dict was passed directly
to PostgreSQL JSONB column without Json() wrapper.

Solution:
- Import Json from psycopg2.extras
- Wrap abilities_json with Json() in INSERT
- Wrap data.abilities with Json() in UPDATE

Same issue as rest_days JSONB fix (commit 7d627cf).

Closes #13

backend/routers/admin_training_types.py

@@ -7,6 +7,7 @@ import logging
 from typing import Optional
 from fastapi import APIRouter, HTTPException, Depends
 from pydantic import BaseModel
+from psycopg2.extras import Json
 
 from db import get_db, get_cursor, r2d
 from auth import require_auth, require_admin
@@ -103,7 +104,7 @@ def create_training_type(data: TrainingTypeCreate, session: dict = Depends(requi
             data.description_de,
             data.description_en,
             data.sort_order,
-            abilities_json
+            Json(abilities_json)
         ))
 
         new_id = cur.fetchone()['id']
@@ -153,7 +154,7 @@ def update_training_type(
             values.append(data.sort_order)
         if data.abilities is not None:
             updates.append("abilities = %s")
-            values.append(data.abilities)
+            values.append(Json(data.abilities))
 
         if not updates:
             raise HTTPException(400, "No fields to update")