Double the far-zoom heat spots so they read as spots

At 10 km per pixel each fire was a marker-sized spot that faded into the
imagery from the globe view. A 2048 px grid with the same one-pixel blur
makes every spot exactly twice as wide (~60 km for a lone weak fire),
still separate, and the build is three times faster.

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

@@ -4,6 +4,6 @@
   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 shows a Snap Map–style heatmap in the same colors instead of squares,
-  one marker-sized spot per fire, empty where nothing burns. The filter applies once before rendering, so markers, cards, the heatmap, context and the top-fires query agree; share
+  one distinct spot per fire, 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).