Mark fallback NP computation for future removal

site/src/components/ActivityDetail.svelte

@@ -112,8 +112,8 @@
   $: galleryImages = (detail?.custom as any)?.images as string[] ?? [];
 
 
-  // Coggan NP from timeseries — mirrors the Python implementation in metrics.py.
-  // Used as fallback for activities extracted before np_power_w was added to the JSON.
+  // TODO(cleanup): fallback NP from timeseries — remove once all activities have been
+  // re-extracted with np_power_w baked into the JSON. Mirrors metrics.py → _np_power().
   function computeNpFromTimeseries(ts: Timeseries): number | null {
     const { t, power_w } = ts;
     if (!power_w || !t || t.length < 30) return null;