studio: finish UI polish pass and document themes + nav gizmo

Viewport shading toolbar: a thin divider now separates the world-layer
overlay toggle from the Wireframe/Solid/Material shading buttons, so the
two groups read as distinct sets of controls rather than a run of icons.

Properties tab column: the open tab gets a blue accent bar on its left
edge, and the tab icons are theme-aware (the active and hovered icons use
the theme's text colour, the rest its muted colour) instead of hardcoded
greys that washed out on light themes.

README and the Studio guide now cover the navigation gizmo (drag to orbit,
click an axis to snap to that view) and the Window > Theme palette.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/studio-guide.md

@@ -46,6 +46,9 @@ Layout** puts everything back; **Ctrl+Space** fills the window with the 3D Viewp
 (a big view with Properties on the World tab) and **Headset** (Properties on the Headset tab). Studio remembers
 your layout between runs.
 
+**Themes.** **Window > Theme** recolours the whole interface, from dark to light, using the palette from the MetaDB
+site. The choice is saved and comes back next time.
+
 ## Opening a home
 
 - **File > Open...** (Ctrl+O), or drop a file on the window. It opens:
@@ -61,7 +64,8 @@ your layout between runs.
 
 | Do this | With |
 |---|---|
-| Orbit | middle-drag, or Alt + left-drag |
+| Orbit | middle-drag, Alt + left-drag, or drag the axes gizmo in the top-right corner |
+| Snap to a view (top, front, side...) | click an axis ball on the gizmo (or the Numpad: 1/3/7 front/side/top, Ctrl for the opposite) |
 | Pan | Shift + middle-drag |
 | Zoom | mouse wheel, or Ctrl + middle-drag |
 | Fly | hold the right mouse button + W A S D, Q / E down / up (wheel: speed, Shift: 4x) |