fix: label Clear filters for assistive technology

[janicduplessis]

Description

The Trails empty-results action was announced only as “Clear filters.” Give it the explicit assistive-technology label “Clear all trail filters” while leaving its visible text and filter-reset behavior unchanged.

Closes #1

Test plan

• On the Stim-owned iOS simulator, searched for no-matching-trail, then selected Adirondacks and Hard to exercise all three filter types in the empty-results state.
• Verified the action’s accessibility-tree label changes from Clear filters to Clear all trail filters.
• Pressed the labeled action and verified the search reset to Search trails, All regions and Any level were selected, and the list returned to 200 trails.

Before

Accessibility tree: [button] "Clear filters"

After

Accessibility tree: [button] "Clear all trail filters"