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/claude/invariants-math-channels.md

@@ -307,7 +307,7 @@ the assertion: `finite` must be about `M` minus the hole share, and `finite=0` b
   non-activatable -- a heading that highlighted under the pointer would read as a row you can plot --
   and it carries the `+` that creates a channel, appended even when there are none, because a `+` that
   waited for a channel to exist could never create the first one. A math row's menu is *Edit graph…*,
-  *Default colour*, *Delete*: no Information and no Calibrate, because calibration is applied at
+  *Default colour*, *Delete*: no Information and no Gain/Offset rows, because calibration is applied at
   ingest and a derived channel has no stream to describe, and no rename, because the node editor owns
   a channel's name and unit and a second place to change them would be a second answer to the same
   question. A row's tick is the channel's own switch and must reach `App::math` -- the copy the