Fix software-compliance report + relationshiptypes zero-dates

- Add applications.isrequired (model + migration 7c02 + create/update + form
  checkbox). The software-compliance report compared required apps against
  installs but no such flag existed, so it 500'd; now it works.
- Repair relationshiptypes rows with 0000-00-00 createddate/modifieddate
  (partof/connectedto) to real timestamps.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shopdb/core/api/applications.py

@@ -131,6 +131,7 @@ def create_application():
         ishidden=data.get('ishidden', False),
         isprinter=data.get('isprinter', False),
         islicenced=data.get('islicenced', False),
+        isrequired=data.get('isrequired', False),
         image=data.get('image')
     )
 
@@ -168,7 +169,7 @@ def update_application(app_id: int):
     fields = [
         'appname', 'appdescription', 'supportteamid', 'isinstallable',
         'applicationnotes', 'installpath', 'applicationlink', 'documentationpath',
-        'ishidden', 'isprinter', 'islicenced', 'image', 'isactive'
+        'ishidden', 'isprinter', 'islicenced', 'isrequired', 'image', 'isactive'
     ]
 
     changes = {}