fix(capture): rotate length-axis rectangle and scale from mask span

Length axis keeps the approved mask, replaces Flip 180 with a ± angle
slider, and sets scale from wood span along the approved direction rather
than bbox.longSidePx. Widths still sample every 6 in perpendicular to that
axis.

frontend/src/App.svelte

@@ -64,7 +64,7 @@
     {:else if cap.k === 'axis'}
       <AxisPanel
         state={cap}
-        rotateAxis={session.rotateAxis}
+        setAxisAngle={session.setAxisAngle}
         approveAxis={session.approveAxis}
         back={session.back}
       />