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/sketch/src/model.rs

@@ -698,10 +698,8 @@ impl Sketch {
             | Symmetric { l, .. }
             | PointLineDistance { l, .. }
             | LinearDiameter { l, .. } => need_line(l)?,
-            ArcLength { c, .. } => {
-                if !matches!(self.curves.get(c).map(|c| &c.kind), Some(CurveKind::Arc { .. })) {
-                    return Err(SketchError::WrongKind(name(c), "arc length needs an arc".into()));
-                }
+            ArcLength { c, .. } if !matches!(self.curves.get(c).map(|c| &c.kind), Some(CurveKind::Arc { .. })) => {
+                return Err(SketchError::WrongKind(name(c), "arc length needs an arc".into()));
             }
             Smooth { a, b } => {
                 let ends = |i: usize| self.curves.get(i).and_then(|c| c.kind.ends());
@@ -730,10 +728,8 @@ impl Sketch {
                     return Err(SketchError::WrongKind(name(a), "tangent needs a circle or arc".into()));
                 }
             }
-            Equal { a, b } => {
-                if is_line(a) != is_line(b) {
-                    return Err(SketchError::WrongKind(name(b), "equal needs two lines or two circles/arcs".into()));
-                }
+            Equal { a, b } if is_line(a) != is_line(b) => {
+                return Err(SketchError::WrongKind(name(b), "equal needs two lines or two circles/arcs".into()));
             }
             Coincident { p, q } if p == q => return Err(SketchError::Invalid("a point is always coincident with itself".into())),
             _ => {}