Show active-filter state and quick-clear in schedule header

[JacobCoffee]

Summary

• When track filters are active (`excludeTracks` non-empty), the funnel icon in the schedule header switches from outline → filled and turns PyCon 2026 pink (#DD04D2).
• A `close-circle` button appears before the funnel; tap clears all filter state (in-memory, storage, schedule refresh) in one shot.
• No header change at all when no filters are active.

Addresses the "I have everything unselected except one track and I can't tell filters are on" confusion + "I can't quickly reset filters" friction.

Test plan

• No filters applied → header looks identical to before (outline funnel, gray)
• Open filter modal, exclude a track, confirm → funnel fills + goes pink, close-circle button appears
• Tap close-circle button → all filters cleared, icons return to default, schedule shows all tracks again
• Re-open the app → cleared state persists (storage was updated)
• Reopen filter modal → all tracks shown as included