* Validate id types in LinkedFiles getSourceProject
Require source_project_id and v1_source_doc_id to be primitives before
querying Mongo, rejecting anything else with BadDataError.
* Validate refreshLinkedFile request params and body
Route refreshLinkedFile through parseReq with a schema requiring
project_id and file_id to be ObjectIds and typing the request body.
* Use well-formed ObjectIds in LinkedFilesController tests
Give the shared test setup valid ObjectId project_id/parent_folder_id
so parseReq passes and the controller logic is actually exercised, and
fail the tests if next is called unexpectedly.
* Use ObjectId file ids in v1 linked-file acceptance fixtures
The refresh route now validates file_id as an ObjectId, so the v1
not-imported fixtures need well-formed ids to reach the refuse-to-refresh
path (409) instead of failing id validation (404).
GitOrigin-RevId: d78b3664e825c6bb25ab2e363e5094b9212db307
Jakob Ackermann