Snap 3D bridge lines to points on other sketch planes (#229)

* Snap 3D bridge drawing to points on visible sketch planes

* Keep cross-sketch point picks out of sketch tools

`pick()` returned every visible sketch's points while 3D drawing was on,
so `sketch_point_at` and the sketch tools could take another sketch's
point as an active-sketch local point plus id (flattening it or making a
bad coincident reference). `pick()` is local again; the bridge snap uses
`pick_3d` explicitly and hover mirrors it for feedback. `sketch_point_at`
also ignores foreign points defensively.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* test(sketch3d): check local point scope with a sketch tool active

Main's Project preselection fix now offers other sketches' points to idle
selection, so assert the local scope where it still applies.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* style: rustfmt

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: bherbruck <brennen.herbruck@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/book/src/guide/sketching.md

@@ -81,6 +81,10 @@ it smoothly. Right-click finishes an ordinary natural fit. Offset accepts both e
 handles and dense fitted curves; the second click sets the side and distance from the curve.
 
 Enable **3D Sketch** in the Sketch Palette to draw lines, fit splines and points off the plane.
+While placing these points, you can snap to points on other visible sketches. For a bridge
+line, start Line and click an endpoint on each source sketch; each endpoint uses its source
+plane, even when that plane differs from the active sketch. These snaps capture positions;
+they do not create associative links to the source points.
 New 3D geometry follows its sketch's component placement, including the selected occurrence
 and pending position changes. Click a drawn fit point to show its move triad; its arrows move
 along world X, Y and Z. Scripts also supply world coordinates to `sketch.line3d`,