Replace PanelSpanButtons with SampleRateOverlay overlay

- Add SampleRateOverlay.pas: TCustomControl overlay (top-left of spectrum)
  with hide-panel button and 6 span buttons (48k–1536k), same hit-test
  pattern as VfoOverlay
- Consolidate toolbar: move PanelTopVfoGroup and PanelSMeterRight into
  PanelToolbar (height 72) instead of floating on the form
- Remove PanelSpanButtons (alTop spacer) that caused the ~1cm black strip
  at the top of the spectrum
- Add separator line inside PanelToolbar anchored to its bottom edge,
  with 16px left/right margins
- Fix left panel blocks starting Y offset (was 38, now 0)

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

ewsdr.lpi

@@ -95,6 +95,10 @@
         <Filename Value="VfoOverlay.pas"/>
         <IsPartOfProject Value="True"/>
       </Unit>
+      <Unit>
+        <Filename Value="SampleRateOverlay.pas"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
       <Unit>
         <Filename Value="AudioOutput.pas"/>
         <IsPartOfProject Value="True"/>