Chore: enable flake8-bugbear (B) default-subset ruff rules

3 B009 (getattr with a constant string, rewrite as attribute access)
hits autofixed. 7 B017 (assert blind Exception) hits: one narrowed
to the actual ValueError raised by bulk_edit.edit_pdf, the other six
suppressed with noqa since the code under test genuinely raises (or
a mock genuinely injects) a bare Exception, so a narrower assertion
would be wrong.

Only the 29 B codes ruff 0.16 enables by default; the rest of
flake8-bugbear needs a separate, deliberate decision.

src/documents/tests/test_classifier.py

@@ -783,7 +783,7 @@ class TestClassifier(DirectoriesMixin, TestCase):
 
         Path(settings.MODEL_FILE).touch()
         mock_load.side_effect = Exception()
-        with self.assertRaises(Exception):
+        with self.assertRaises(Exception):  # noqa: B017 - mock injects a bare Exception
             load_classifier(raise_exception=True)