Merge origin/main into german/navara

Brings the Active Fires intensity work: the FRP filter, the confidence
switch, the ember-to-white-hot ramp and the far-zoom heatmap.

The filter, switch and ramp work on both engines. The heatmap drapes on
Cesium through the layer's Cesium renderer, which also fades the markers
across the hand-off; it goes with that renderer on an engine switch and is
built again on the next Cesium globe. Navara keeps heat cells for the far
bands, now coloured on the FRP ramp.

docs/CURRENT-STATE.md

@@ -2323,6 +2323,62 @@ Generated style sliders use the same name as their visible parameter label.
 The first-run suppression checkbox keeps its native wrapping label, so its
 accessible name remains "Don't show this again". Control behavior is unchanged.
 
+## Active Fires intensity filter and color ramp
+
+Every FIRMS detection is colored by fire radiative power on a six-stop ember →
+white-hot ramp: dark ember from 0 MW, red from 5, flame from 20, orange from
+50, gold from 100 and pale white-hot from 300 MW (`FRP_RAMP` in
+`src/data/firmsIntensity.js`). Each stop is lighter than the one below and
+none is a cold hue, so the brightest marks are the strongest fires; ~90% of
+detections are under 20 MW and stay dim red. Glow sprites and fire-card
+accents read that ramp; confidence and brightness do not affect the color.
+
+At far zoom (camera above ~4,500 km) the layer drapes a Snap Map–style
+heatmap instead of individual markers: the shown detections are linearly binned
+(each detection's weight shared between the four nearest pixel centres, so spots
+sit at the true position and stay round) on a
+global 4096 × 2048 grid (≈10 km per pixel), each weighted by its FRP in megawatts (so heat is
+radiated power, and raising the FRP slider does not dim areas where strong fires
+burn, and a cluster of detections reads brighter than one), Gaussian-blurred by one
+pixel so each fire stays a distinct spot about the size of its marker,
+normalized on a log scale against the 99.5th percentile and mapped through the
+same hues, from a bright red edge through orange and gold to a pale
+white-hot core. The edge starts more than half opaque, so regions far below
+the hottest ones still read over forest and savanna imagery. Nothing is painted where
+nothing burns (`src/data/firmsHeatRaster.js`). It is one full-globe imagery
+tile on the active imagery host (`src/layers/firms/heatImagery.js`), rebuilt
+on each data refresh or filter change (the first far-band paint at once,
+later ones 150 ms after the last change). Heatmap and markers are both kept
+built at every zoom and cross-fade by camera height between 3,600 and
+5,400 km, every frame, so a fast zoom never shows a gap: the heatmap fades by
+imagery `alpha` (a hidden Cesium imagery layer is unmapped from the globe
+tiles and re-mapped late when shown), the markers by sprite alpha, and the
+marker collection is hidden once the heatmap is whole. The 750–4,500 km
+markers band draws up to 40,000 detections (the strongest in the padded
+view), so the weak fires the heatmap shows stay on screen as markers when it
+fades out; it reads each marker's already-built anchor instead of the ground
+floor cache, which only the close band warms. "N FIRES" cards from a 2° / 1° aggregation still label the hottest
+areas; their accent is the strongest fire's FRP color.
+Re-enabling Active Fires keeps the retained heat imagery hidden when the current
+filtered set is empty, including while a new snapshot is pending.
+
+The Active Fires row carries a "Fire intensity (FRP)" slider on a log scale
+whose track is painted with the ramp and ticked at the same six values (its
+value reads "All" or "≥ N MW"), a "Confidence" switch with All / Nominal+ /
+High, and an "N of M shown" counter. The default is 0 MW and
+All, because many of the strongest detections are rated low confidence. The
+filter runs once in `ingestion.applyFilter()` before rendering, so markers,
+cards, the heatmap, the shared context store, the top-fires query and the
+analyst records all see one filtered set; a selected fire that no longer passes
+is deselected. The layer state keeps both options under the `w` (`local-firms`)
+share token as `f` (whole megawatts, 0–10,000) and `c` (`a`, `n`, `h`),
+including the short share codec; a link without them restores the defaults.
+
+The `get_active_fires` tool accepts its own `min_frp_mw` and `confidence`
+(`all`, `nominal`, `high`) arguments, independent of the panel's setting, and
+names the applied criteria in its notes. Stale-snapshot and missing-source
+reporting are unchanged.
+
 ## FIRMS source status
 
 The FIRMS CSV parser rejects impossible acquisition calendar dates before the proxy filters records to the trailing 24 hours, while retaining valid UTC acquisition times.