Rework 3D view navigation:
- Turntable / lock-horizon orbit: horizontal drag yaws about world +Z,
vertical drag pitches about the horizontal camera-right axis, so the
view never banks. Pitch is pole-clamped but the straight-down default
view can still be tilted out of.
- Orbit centre: the selection's centre when something is selected,
otherwise the point under the cursor — no longer only the file centre.
The camera revolves rigidly about the pivot, so it stays put on screen
and the view doesn't jump.
- Mouse scheme: Zoom = wheel, Pan = MMB, Rotate = Shift+MMB. Right-drag
no longer orbits (right-click stays context menu / Enter). Floating
viewports orbit with Shift+MMB too.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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