printedparts: QR label with gage tag + revision; record taken rev

Label switches from CODE128 to a QR encoding 'TAG|rev' (gage lab tag + latest
print-file revision), so a physical part carries which revision it was printed
from - short payload stays low-version + reliable at 0.5in (margin quiet zone,
EC M, no logo). Item exposes latestrevision; kiosk strips the |rev to resolve
and records the scanned revision on the take (migration 0004 adds
printeditemtransactions.revision) for traceability of which rev was consumed.
Manual entry records a null revision.

plugins/printedparts/models/printeditem.py

@@ -46,11 +46,20 @@ class PrintedItem(BaseModel):
     def islowstock(self):
         return self.quantityonhand <= self.lowstockthreshold
 
+    @property
+    def latestrevision(self):
+        """Highest print-file revision, or None when the item has no files.
+        Stamped on the label QR so the physical part carries its source rev."""
+        from sqlalchemy import func
+        return db.session.query(func.max(PrintedItemFile.revision)).filter(
+            PrintedItemFile.printeditemid == self.printeditemid).scalar()
+
     def to_dict(self):
         return {
             'printeditemid': self.printeditemid,
             'itemcode': self.itemcode,
             'gagelabtag': self.gagelabtag,
+            'latestrevision': self.latestrevision,
             'itemname': self.itemname,
             'itemdescription': self.itemdescription,
             'imageurl': self.imageurl,
@@ -82,6 +91,10 @@ class PrintedItemTransaction(BaseModel):
     employeesso = db.Column(db.String(20), nullable=False, index=True)
     employeename = db.Column(db.String(120))
     reason = db.Column(db.String(255))
+    # Print-file revision the physical part carried, captured from the label QR
+    # at take time (null for manual entry / pre-QR labels). Traceability of
+    # which revision was actually consumed.
+    revision = db.Column(db.Integer)
     transactiondate = db.Column(db.DateTime, nullable=False, default=_utcnow,
                                 index=True)
 
@@ -94,6 +107,7 @@ class PrintedItemTransaction(BaseModel):
             'employeesso': self.employeesso,
             'employeename': self.employeename,
             'reason': self.reason,
+            'revision': self.revision,
             'transactiondate': self.transactiondate.isoformat() + 'Z' if self.transactiondate else None,
         }