[TASK] Single-selection folder list view is a tab trap (every row tabbable)

Parent

Follow-up from #32591 / PR #37436 (Content Drive keybindings).

Problem

dot-folder-list-view in single-selection mode makes every row a tab stop. A listing of 40
rows is 40 presses of Tab to get past, which is the tab-trap #32591 fixed for Content Drive, still
present for the single-selection consumer (the asset selection dialog).

Cause

PrimeNG's SelectableRow.setRowTabIndex() short-circuits to "every row is tabbable" whenever the
selection is empty, before it ever consults the table's anchor. An empty selection is the
permanent resting state of a single-selection list, so the anchor #37436 drives is never read and
the roving tab stop never applies.

Confirmed structural rather than a timing artifact by letting a second render settle.

Scope decision in #37436

Out of scope, deliberately: FR-001 was amended to multiple-selection listings only. The behaviour is
pinned by a no-regression test so it cannot change silently —
should leave single-selection tab behaviour exactly as it was in
dot-folder-list-view.component.spec.ts. That test asserts today's trunk behaviour, so whoever fixes
this will see it fail and be pointed here.

What "done" looks like

• One tab stop in single-selection mode, roving with focus, exactly as in multiple
• The no-regression test above updated (not deleted) to assert the new behaviour
• The asset selection dialog checked, since it is the consumer

Where

• core-web/libs/ui/src/lib/components/dot-folder-list-view/dot-folder-list-view.component.ts
  (#applyRovingTabStop, #seedTabStop)

Start in core-web/libs/ui/src/lib/components/dot-folder-list-view/dot-folder-list-view.component.ts, reading #applyRovingTabStop and #seedTabStop, then run dot-folder-list-view.component.spec.ts. Update the named no-regression test to cover the new single-selection behavior, and verify the asset selection dialog has one roving tab stop.