fix: Fix AttributeError in report_categories

- Add .label('category') to SQLAlchemy query for proper Row attribute access
- Change filter_by to filter() for better NULL handling

Fixes 500 error on /raporty/struktura-branzowa

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app.py

@@ -8740,7 +8740,7 @@ def report_categories():
     try:
         # Grupowanie po kategoriach
         category_counts = db.query(
-            Company.category,
+            Company.category.label('category'),
             func.count(Company.id).label('count')
         ).group_by(Company.category).all()
 
@@ -8749,8 +8749,8 @@ def report_categories():
         categories = []
         for cat in category_counts:
             cat_name = cat.category or 'Brak kategorii'
-            examples = db.query(Company.name).filter_by(
-                category=cat.category
+            examples = db.query(Company.name).filter(
+                Company.category == cat.category
             ).limit(3).all()
 
             categories.append({