docs(fires): describe the far-zoom heatmap

Co-Authored-By: Claude Opus 5.5 <[email protected]>

changelog.d/1426-fire-intensity-filter.md

@@ -2,8 +2,8 @@
   cold → hot ramp (blue · teal · lime · amber · orange · red at 0 · 5 · 20 ·
   50 · 100 · 300 MW), and add a log-scale minimum-FRP slider whose track is the
   ramp, an All / Nominal+ / High confidence switch and an "N of M shown"
-  counter to the layer row. Far-zoom heat cells keep a warm density fill
-  (lime · amber · red). The filter applies once before rendering, so
-  markers, cards, heat cells, context and the top-fires query agree; share
+  counter to the layer row. Far zoom shows a Snap Map–style heatmap instead
+  of squares, empty where nothing burns. The filter applies once before
+  rendering, so markers, cards, the heatmap, context and the top-fires query agree; share
   links keep it (`w` token: `f`, `c`), and `get_active_fires` takes matching
   `min_frp_mw` and `confidence` arguments. Default 0 MW / All (gekh, #1426).