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.

shopdb/api/__init__.py

@@ -45,6 +45,7 @@ from shopdb.core.models import (
     AssetRelationship,
     RelationshipType,
     User,
+    Role,
 )
 
 # Response + pagination helpers for plugin API blueprints
@@ -271,6 +272,7 @@ __all__ = [
     'send_email',
     'send_alert',
     'User',
+    'Role',
     # CMMC USB check-in/out database
     'cmmc_usb_connection',
 ]