ui: a signal's page shows gain and offset as aligned rows with a pencil each, replacing Calibrate

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/USER-GUIDE.md

@@ -66,8 +66,8 @@ the same signal twice, or onto another badge to reorder the badges. The colour i
 the same signal is the same colour wherever it appears.
 
 Clicking a signal's badge opens its own page: the colour, **Plot on** buttons for the rows, and
-**Calibrate** — gain and offset, applied at ingest, so the measurements and the export carry the same
-numbers the plot shows.
+**Gain** and **Offset**, shown as two aligned numbers with a pencil button each that edits that one value.
+They are applied at ingest, so the measurements and the export carry the same numbers the plot shows.
 
 ## 4. The window and navigation