Admin Users: persist requested storage, rename and regroup filters, add clear action - #6096

"Has Studio edits" matched any Change row the user ever created, so it
reported activity rather than edits; renamed to "Has Studio activity" in
the filter row and the CSV header.

On wide viewports the two checkboxes sat in separate quarter-width
columns, leaving a large gap between them. They now share one half-width
flex row alongside a "Clear filters" action, which resets every filter
while preserving pagination and sorting. The action is enabled only once
a filter differs from the default its control already displays.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

The spec drove the component through wrapper.vm — assigning filters and
reading computed properties — so it asserted internals rather than
behaviour. Rewritten against Vue Testing Library, per the frontend
testing guidelines, querying by label and role and asserting on the
dispatched fetch payload.

Two problems surfaced once the queries went through the accessibility
tree. "Clear filters" used appearance="basic-link", which KButton
renders as an anchor; disabled is not a valid attribute there and
KButton's click handler does not guard on it, so the greyed-out link was
still focusable and still fired. It is now shown only when there is
something to clear. Studio's IconButton passes ariaLabel="text" unbound,
leaving icon buttons with no usable accessible name, so those two are
still reached by their existing data-test hooks.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Replace the Vuetify layout and form controls above the users table with
their Kolibri Design System equivalents: VLayout/VFlex become KGrid and
KGridItem, VSelect becomes KSelect, VTextField becomes KTextbox with a
prepended KIcon, and VProgressLinear becomes KLinearLoader.

KSelect emits `select` only on user action, so the filters bind `:value`
and `@select` rather than v-model, which would otherwise write the
defaults back into the URL and undo "Clear filters".

VDataTable, CountryField and UserItem still wrap Vuetify and are left for
a later pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

The component mixed an Options API shell with composables. Move it wholly
into `<script setup>`: the Vuex getters become computeds over useStore,
routerMixin's tab title becomes an onMounted call to updateTabTitle, and
the responsive headers become a plain function of the breakpoint.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Four comments restated what the code already said: two doc blocks naming
their own helpers, and a pointer to renderWithFilters repeated above two
calls to it. The remaining comments each cite behaviour of code outside
this file that a test has to work around.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CountryField gains fullWidth, which switches its own max-width from 500px
to 100%. KTextbox caps the inner UiTextbox at max-width: 400px, which a
pass-through class cannot reach, so it is overridden through the
component's appearanceOverrides prop.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>