fix(ui): keep panel scroll position through rail layout passes (#731)

The right-rail layout pass lifts the Context, CCTV, Weather and Recent
Imagery panel scrollers to measure their natural heights, which clamps
their scroll offset to zero, but it only restored scrollers tagged
data-rail-scroller. A layer that refreshes its Layers-panel row every
second snapped the Context panel back to the top while scrolling. Tag
every lifted scroller and pin the pairing with a test that reads the
measuring CSS.

Co-authored-by: Bilawal Sidhu <[email protected]>

src/ui/templates/context.html

@@ -2,7 +2,7 @@
   <aside id="right-context-rail">
     <div id="weather-panel" class="panel-collapsible" data-panel-id="weather-panel" hidden>
       <div class="panel-glow"></div>
-      <div class="weather-panel-inner">
+      <div class="weather-panel-inner" data-rail-scroller>
         <div class="panel-header">
           <span class="panel-title">WEATHER</span>
           <span id="weather-panel-count" aria-label="Active weather products">0</span>
@@ -14,7 +14,7 @@
     </div>
     <div id="recent-imagery-panel" class="panel-collapsible" data-panel-id="recent-imagery-panel" hidden>
       <div class="panel-glow"></div>
-      <div class="recent-imagery-panel-inner">
+      <div class="recent-imagery-panel-inner" data-rail-scroller>
         <div class="panel-header">
           <span class="panel-title">RECENT IMAGERY</span>
           <span id="recent-imagery-panel-count" aria-label="Imagery days in the box"></span>
@@ -26,7 +26,7 @@
     </div>
     <div id="global-context-panel" class="panel-collapsible collapsed" data-panel-id="global-context-panel">
       <div class="panel-glow"></div>
-      <div class="global-context-panel-inner">
+      <div class="global-context-panel-inner" data-rail-scroller>
         <div class="panel-header">
           <span class="panel-title">CONTEXT</span>
           <span class="panel-divider"></span>