algo.md was read at runtime via File.read! but isn't included in
the release. Use @external_resource + compile-time module attribute
to bake the HTML into the module.
- Port grid square rendering from gridmap-web with toggle control
- Consolidate band selector, grid toggle, data timestamp, and links
into unified control panel
- Add "How this works" (/algo) and "Submit a QSO" (/submit) links
- Add back-to-map link on algo page
- Darken range circles for visibility over propagation overlay
- Fix popup blocking double-click zoom with pointer-events passthrough
- Prevent control panel from intercepting map click/scroll events
