Fix viewport input leaking through dialogs

Use egui pointer ownership for viewport navigation and picking, view-cube
interaction, and sketch-dimension hover. Cover scrolling, model selection,
and cube interaction under floating dialogs, including after they close.
Shield constraint glyph and move-gizmo highlights from overlapping UI too.

Clear strict Clippy warnings and use the same saved path in the recent-file
scenario on Windows and Unix.

Fixes #87

crates/engine/src/cmd/sketch_modify.rs

@@ -520,7 +520,7 @@ fn fillet_corner(sk: &mut Sketch, p: &Value, r: f64, cmd: &str) -> Result<(usize
     let u = (pa - pc).normalized().ok_or_else(|| bad(cmd, "degenerate line"))?;
     let v = (pb - pc).normalized().ok_or_else(|| bad(cmd, "degenerate line"))?;
     let half = 0.5 * u.cross(v).atan2(u.dot(v)).abs();
-    if half < 1e-6 || half > std::f64::consts::FRAC_PI_2 - 1e-9 {
+    if !(1e-6..=std::f64::consts::FRAC_PI_2 - 1e-9).contains(&half) {
         return Err(bad(cmd, "the lines are parallel"));
     }
     let d = r / half.tan();