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/__init__.py

@@ -1,5 +1,11 @@
 """Printedparts plugin models."""
 
-from .printeditem import PrintedItem, PrintedItemTransaction, TRANSACTION_TYPES
+from .printeditem import (
+    PrintedItem,
+    PrintedItemTransaction,
+    PrintedItemFile,
+    TRANSACTION_TYPES,
+)
 
-__all__ = ['PrintedItem', 'PrintedItemTransaction', 'TRANSACTION_TYPES']
+__all__ = ['PrintedItem', 'PrintedItemTransaction', 'PrintedItemFile',
+           'TRANSACTION_TYPES']