printedparts stage 15: print-file revision history + role-based alerts

printeditemfiles lands as the plugin's first incremental migration
(0002 on the plugin chain - the ADR-008 payoff). Revisions are
append-only per item: upload assigns the next number, records the
uploader from the JWT, enforces an extension allowlist and a 100 MB
cap; download serves the original filename; a permission-gated delete
covers wrong-file mistakes. The detail page gains the revision table
with a current badge. Unique storedfilename is sized 191 so the index
fits MySQL's 767-byte prefix - the per-plugin chain does not apply the
core env's ROW_FORMAT hook.

Alert recipients gain roles: Role joins the 0.13.0 surface, a role
picker on the settings page, and every active member of the selected
roles is folded into the deduped recipient list.

plugins/printedparts/models/printeditem.py

@@ -93,3 +93,43 @@ class PrintedItemTransaction(BaseModel):
             'reason': self.reason,
             'transactiondate': self.transactiondate.isoformat() + 'Z' if self.transactiondate else None,
         }
+
+
+class PrintedItemFile(BaseModel):
+    """One uploaded revision of an item's print file (STL/3MF/gcode/...).
+
+    Revisions are append-only per item: uploading assigns the next revision
+    number and never replaces earlier files, so the history of what was
+    actually printed stays reconstructible. The current file is simply the
+    highest revision.
+    """
+
+    __tablename__ = 'printeditemfiles'
+
+    fileid = db.Column(db.Integer, primary_key=True)
+    printeditemid = db.Column(
+        db.Integer,
+        db.ForeignKey('printeditems.printeditemid', ondelete='CASCADE'),
+        nullable=False, index=True)
+    revision = db.Column(db.Integer, nullable=False)
+    filename = db.Column(db.String(255), nullable=False,
+                         comment='Original upload name, used for download')
+    storedfilename = db.Column(db.String(191), nullable=False, unique=True,
+                               comment='191: unique index fits the 767-byte MySQL prefix')
+    filesize = db.Column(db.Integer, nullable=False)
+    uploadnote = db.Column(db.String(255),
+                           comment='What changed in this revision')
+    uploadedby = db.Column(db.String(80), nullable=False,
+                           comment='Username of the uploader')
+
+    def to_dict(self):
+        return {
+            'fileid': self.fileid,
+            'printeditemid': self.printeditemid,
+            'revision': self.revision,
+            'filename': self.filename,
+            'filesize': self.filesize,
+            'uploadnote': self.uploadnote,
+            'uploadedby': self.uploadedby,
+            'uploadeddate': self.createddate.isoformat() + 'Z' if self.createddate else None,
+        }