docs(fires): current-state note and changelog fragment for the intensity filter (#1426)

Describe the six-stop FRP ramp, the slider / confidence switch / counter,
the single filter point, the share-token options and the tool arguments in
docs/CURRENT-STATE.md, and add changelog.d/1426-fire-intensity-filter.md as
CONTRIBUTING asks for runtime changes.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docs/CURRENT-STATE.md

@@ -2054,6 +2054,30 @@ 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 cold →
+hot ramp: blue from 0 MW, teal from 5, lime from 20, amber from 50, orange from
+100 and red from 300 MW (`FRP_RAMP` in `src/data/firmsIntensity.js`). Heat
+cells, glow sprites and card accents read the same ramp; confidence and
+brightness do not affect the color.
+
+The Active Fires row carries a minimum-FRP slider on a log scale whose track is
+painted with the ramp and ticked at the same six values, an All / Nominal+ /
+High confidence switch, 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, heat cells, 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.