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>

docs/book/src/guide/shortcuts.md

@@ -39,5 +39,6 @@ Mouse and touch:
 | Click again on the same spot | select the next thing under the cursor (click cycling) |
 | Hold the left button still (long-press on touch), or right-click › Select Other… | list everything under the cursor to pick from |
 | Double-click a sketch curve or edge | select its chain or tangent loop |
+| Double-click the middle button | go Home: the home view, framing everything shown (Preferences › Navigation › Middle double-click: Home, Fit or Off) |
 
 Help › Keyboard Shortcuts in the app lists the current bindings, including any you changed.