Adds a "Radio location" section to the coverage form with an embedded
Leaflet map. The marker starts at the parent site's coordinates and
the user can drag it to the actual radio location. A "Use site
location" button clears the override.
- New CoverageLocationPicker hook in assets/js/app.ts: creates the
map, draggable marker, and pushes "location_picked" {lat, lon} on
dragend. Re-creates the marker when the user picks a site that
initially had no coords.
- form.html.heex: location section with map div (phx-hook), readout
("lat, lon - override" if set), and reset button. Hidden inputs for
latitude_override / longitude_override so the form's params always
carry the chosen coordinates.
- form.ex: handle_event "location_picked" updates the override fields
in the changeset; "use_site_location" clears them. Helper functions
radio_marker_lat/lon walk the form values, falling back to the
selected site.
CI test gate fix:
- Worker test now requires GDAL CLI tools to write GeoTIFF + PNG.
test_helper.exs detects whether gdal_translate / gdaldem are on
PATH; when missing (CI's lean test image), :requires_gdal tagged
tests are excluded. Locally with brew install gdal they still run.