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/models/application.py

@@ -53,6 +53,10 @@ class Application(BaseModel):
     ishidden = db.Column(db.Boolean, default=False)
     isprinter = db.Column(db.Boolean, default=False)
     islicenced = db.Column(db.Boolean, default=False)
+    isrequired = db.Column(
+        db.Boolean, default=False,
+        comment='Required on all PCs (drives the software-compliance report)'
+    )
     image = db.Column(db.String(255))
 
     # Relationships