Home and Fit frame what is shown now; middle double-click goes Home (#701)

Home, Fit, the orbit pivot and the scene's depth range counted sketches the view doesn't draw (ones used by an extrude or revolve, ones in hidden components), so after a body moved away from its sketch Home framed the empty spot it came from. They now use the world-space bounds of what is shown now (view::visible_bounds / view::sketch_drawn, viewport::view_bounds). The pick-box cache holds its world state instead of its address. A middle-button double-click goes Home in every preset (Preferences › Navigation: Home, Fit or Off).

Fixes #689

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

crates/ui-egui/src/keymap.rs

@@ -167,7 +167,7 @@ pub fn page(app: &mut SolveApp, ui: &mut egui::Ui) {
             }
             ui.label(
                 RichText::new(
-                    "Select Other: hold the left button still on the model (or right-click › Select Other…) to list everything under the cursor; click again on the same spot to select the next thing there.",
+                    "Select Other: hold the left button still on the model (or right-click › Select Other…) to list everything under the cursor; click again on the same spot to select the next thing there. Double-click the middle button to go Home (Preferences › Navigation).",
                 )
                 .size(11.0)
                 .color(t.text_dim),