Draw mode: slow response time when adding points

[zworkb]

Problem

After implementing auto-handle computation (#71), clicking to add a point in Draw mode has a noticeable delay before the point appears. The more points on the path, the slower it gets.

Likely Cause

compute_handles() is called after every click, which iterates ALL control points and calls azalt_to_radec() / radec_to_azalt() for the overlay refresh. The astropy coordinate conversion is expensive (~50ms per point).

Possible Fixes

1. Only recompute handles for affected points — when adding a point at the end, only recompute handles for the last 3 points (prev, new, and prev-prev), not the entire path
2. Cache coordinate conversions — the overlay refresh converts all RA/Dec → Az/Alt every time, even for points that haven't moved
3. Debounce the overlay refresh — batch multiple updates
4. Profile first — add timing logs to identify the actual bottleneck

Related

• Improve spline fitting in Draw mode (auto-generate Bézier handles) #71 Improve spline fitting in Draw mode