fix(search): complete the query error surface across every endpoint

Four pieces of the same surface:

whoosh-compat's emit() documents a two-part host contract: both a parse
diagnostic and the QueryEmitError/UnsupportedQueryError pair are
user-input errors. Only the latter half was caught; QueryEmitError now
maps to SearchQueryError too. Messages pass through a cleanup that
strips the library's DIVERGENCES.md references and replaces the
fast=True host-configuration advice with user language, so no
library-internal vocabulary reaches a searching user.

The bulk selection paths (bulk edit, the legacy bulk endpoint, bulk
download) reached the backend with no SearchQueryError handler, so a
bad date or number in a selection filter raised straight to a DRF 500.
They now share the search list endpoint's exact mapping (a new
search_query_error_messages helper flattens MultipleSearchQueryErrors
in one place), returning the same 400 body for the same bad query.

QueryParserError means a whoosh-compat parser bug, not user-fixable
input, per its own contract; the list endpoint's blanket handler was
converting it to a generic 400. It now re-raises and surfaces as a 500
that monitoring can see.

All behavior is pinned test-first: bulk edit and bulk download API
tests assert 400s naming the bad value (previously unhandled
exceptions), a unit test pins the QueryEmitError mapping, three
parametrized checks assert no internal vocabulary leaks for the
unsupported query shapes, and a mocked parser-bug test asserts the 500.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WMsn6DgzbvSqh1pwy66VVF

src/documents/tests/test_api_bulk_download.py

@@ -339,3 +339,21 @@ class TestBulkDownload(DirectoriesMixin, SampleDirMixin, APITestCase):
 
         self.assertEqual(response.status_code, status.HTTP_403_FORBIDDEN)
         self.assertEqual(response.content, b"Insufficient permissions")
+
+    def test_bad_search_query_returns_400(self) -> None:
+        response = self.client.post(
+            self.ENDPOINT,
+            json.dumps(
+                {
+                    "all": True,
+                    "filters": {"query": "added:notadate"},
+                    "content": "originals",
+                },
+            ),
+            content_type="application/json",
+        )
+
+        # A user-fixable query error must surface as a 400 naming the bad
+        # value, exactly like the search list endpoint, never a 500.
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        self.assertIn(b"notadate", response.content)