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/doc/src/sheet.rs

@@ -899,7 +899,7 @@ impl SheetBody {
             return Err(DocError::Invalid("the hem is shorter than its bend".into()));
         }
         // A hem folds back over the face it starts from (toward the bottom unless flipped).
-        let up = !top == flip;
+        let up = top != flip;
         let up = !up;
         self.flanges.push(SheetFlange {
             parent: panel,