Import-API: preserve app-version timestamps in import mode

POST /api/applications/{id}/versions now calls apply_import_timestamps so an
imported version's original dateadded/releasedate survives (was skipped, unlike
the app + install endpoints). No-op outside import mode.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shopdb/core/api/applications.py

@@ -271,6 +271,9 @@ def create_version(app_id: int):
     )
 
     db.session.add(version)
+    # Preserve the legacy release/added timestamps in import mode (no-op
+    # otherwise), so imported version history keeps its original dates.
+    apply_import_timestamps(version, data)
     db.session.commit()
 
     return success_response(version.to_dict(), message='Version created', http_code=201)