Failed and Review: choose the folder filter with the kit select #79

What to build

Choosing a source folder to narrow the failed-items or deletion-review list happens in the kit's select control, and after a choice the keyboard focus stays with that control.

Today the control is hand-built: an open/closed flag in the filter model, an option list painted under the button, and a workaround that re-focuses the trigger and advances to the next tab stop, because the activated option unmounts and focus would otherwise fall back to the window's first stop.

Acceptance criteria

• One source folder is chosen from the kit control, and "all folders" is reachable as a choice, not only as a clear action.
• After a choice, focus stays on the filter control; after a clear, focus stays there too. No fallback to the window's first tab stop.
• The active-filter chip still names the folder on screen and still labels the filtered empty state, and its clear action returns the list to all folders.
• The matching rules are unchanged: a recursive folder includes its subfolders, a non-recursive one includes its direct children only, case handling follows the platform, and a folder that is no longer a source still filters.
• Both list surfaces share this one control, and each keeps its own element ids so their tests do not collide.
• Keyboard-only selection, Escape, and the screen-reader name for each option are covered by the tests.

Notes

The rule logic — which items a selected folder keeps, the label, the empty-state wording — is domain code and stays where it is. This ticket replaces the trigger, the list, and the focus handling.