Adds the cnHeat-style horizontal 'Min RSSI' slider beside the opacity
control. Pixels weaker than the threshold turn fully transparent,
client-side, with no server round-trip — same compute output now
powers an interactive 'where can I get -75 dBm or better' exploration.
- Slider range -100..-40 dBm step 1; -100 disables filtering.
- addCoverageLayer fetches each PNG into a hidden canvas and caches
its ImageData. crossOrigin=anonymous keeps reads tainted-free.
- Each pixel is classified by nearest palette colour (-50/-65/-75/
-85/-95 dBm centres matching Raster.write/3) and dropped if its
dBm is below the threshold. Result re-encoded via toDataURL and
swapped onto the L.imageOverlay via setUrl.
- destroyed() revokes blob URLs and clears the filter cache to
avoid leaks during LiveView nav. Bundle: coverage_hooks chunk
16 KB → 20 KB; main bundle unchanged at 1.2 MB.
- /coverage now renders a full-bleed Leaflet map of every ready
coverage in the org as one composite heatmap; the prior table view
moves to /coverage/list.
- Top-right tower toggle list with Show All / Hide All. Disabled
towers grey out and their overlay/marker drop from the map.
- Bottom-center opacity slider controls all overlays in unison; the
cnHeat dBm legend renders next to it.
- Top-left base-layer toggle (OSM streets / Esri satellite) and a
Nominatim address search bar that drops a marker.
- Click anywhere on the map → Distance Tool side panel with each
tower sorted by distance and the predicted RSSI at that point
(read from each coverage's GeoTIFF via gdallocationinfo). ft/m
unit toggle, NA for out-of-bbox, color-coded by signal quality.
- Backend additions: Coverages.list_ready_for_organization/1,
Coverages.query_point/3, Raster.query_rssi/3 (gdallocationinfo
wrapper with bbox guard, NoData sentinel handling).
- New JS hook MultiCoverageMap manages the layer set, toolbar,
search, opacity, click-to-probe, and live updates via PubSub
(coverage:enabled-changed and coverage:list-changed).
