ui: the sidebar's tabs become one dock; Measure and Signals by keyboard section; session keeps the dock's state

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

README.md

@@ -2915,9 +2915,11 @@ now — they are listed so they are not mistaken for anything else:
   unlocked, because configuring the host is what a first run is for. Each pane's heading also carries its **own switch**, the same control as the
   header bar's button — clicking either moves both — because a pane that is *disabled* while its
   feature is off is a pane whose controls you would otherwise have to leave to turn it back on. The
-  switcher's policy is `wide` and each page has a title and no icon (the switcher's own placeholder icon is hidden). With the math
+  sidebar is one **dock** now, with no tab switcher: the signal list, the cursors and the measurements
+  in one scroller, shown from the start and insensitive until the stream has signals; `m` and `g`
+  scroll it to the cursors and back to the signal list. With the math
   list folded into the signal list under a `MATH` divider whose `+` creates a channel — a derived channel already *is* a channel in
-  the model, so the two lists were the same list drawn twice. A tab is one-of-*N*, so no
+  the model, so the two lists were the same list drawn twice. No
   toggle hides a pane any more: cursors-off **disables** its readout and leaves it in place, and
   trigger-off leaves the trigger panel fully editable — a trigger is configured *before* it is
   switched on, and the locked view says `stream (trigger off)` instead of the settings — and the measurements' and math panes' toolbar toggles are gone with the panes.