Artifacts list: icon crowds the filename

Seen in Task 7927's visual check of the Task page's Artifacts tab (desktop 1440px and mobile 390px): - In the artifact row (`components/tasks/TaskArtifacts.tsx`), the leading file icon's ring sits flush against the filename, with no gap. Give it the same icon-to-label spacing other list rows on the console use. Out of scope: the artifact viewer frame, the tab-landing logic, and any other change to the artifact list. Done means: the row shows a visible gap between the icon and the filename at 390px and 1440px (screenshot in the report), and `./dc check full` is green.

Artifact row: 3px title inset so the filename clears the selected disc's ring (4→7px desktop, 3.5→6.5px at 390px). Visual check done: clear gap at both widths. Quick gate + 110 tests green; PR #6233 queued to merge lane for full gate.