Show active filter summary on the map

## Context
The filter button already changes icon state when filters are active, but the plan defers an active filter summary.

## Scope
- Show a compact summary of active map filters.
- Provide a clear way to clear all filters.
- Keep the summary readable with city, country, postal code, keyword, and radius combinations.

## Acceptance criteria
- Users can tell which filters are active without reopening the sheet.
- Clearing filters updates the map and the icon state.
- The layout works on small iPhone screens.