Fix red develop 1e87d0741613

The merge lane found `develop` red at `1e87d074161302aa585135dca4a487839219c5da` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `frontend-unit-vitest` - … and 10 more: read them in the gate log, as untrusted output The whole gate log: artifact `11072` on lane task 10638. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

Fixed red develop: 10 TaskDetailPage vitest cases still looked for the image-attachment filename as text after #7135 made it a thumbnail; they now assert the Preview control. 127/127 tests and quick gate green. PR #7139 queued to the lane.