feat(capture): tape-line overlay UI replaces axis rectangle (#99)

Pointer-Events pan/zoom/tilt under a fixed black ~2pt line with
rifle-scope end ticks (≥44×44 hit). AxisPanel becomes Tape line step;
session persists tape transform; scale = tick distance / L.
sveltedrag unavailable for Svelte 4 — Pointer Events path used.

frontend/src/App.svelte

@@ -75,6 +75,7 @@
       <AxisPanel
         state={cap}
         setAxisAngle={session.setAxisAngle}
+        setTape={session.setTape}
         approveAxis={session.approveAxis}
         back={session.back}
       />