Adds a bottomleft grid button (MapUtils.addGraticuleControl) to every
map in the app — Meshtastic, MeshCore, Drone, SSTV/ISS, BT Locate,
WebSDR, and Weather Satellite — defaulting to visible. The weather
satellite map's bespoke addStyledGridOverlay() is removed in favour of
the shared implementation. Also updates map-utils.css with button
styles and map-utils.js with the new addGraticuleControl() method.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>