fix: Gizmo picking, stuck drags, scale snapping, parentless local translate and ViewCube colorNeg

[kpal81xd]

Description

Fixes five bugs in the gizmos in src/extras/gizmo:

• Picking: _getSelection reused the same temporary vector for the ray direction and the triangle hit point. After the first hit, every later shape was tested with the wrong ray, so overlapping shapes could pick the wrong axis (for example the X plane when hovering the Y arrow).
• Stuck drag: pointerup was ignored while the gizmo was disabled or the pointer was locked. Disabling the gizmo mid-drag left it dragging, and moving the mouse after re-enabling kept moving the node. The release now always ends the drag.
• Scale snapping: ScaleGizmo snapped before dividing by the gizmo's screen scale, so the snap step changed with camera distance. It now snaps the scale factor itself, so snapIncrement = 1 always gives whole-number steps.
• Parentless local translate: in local coordinate space, a node with no parent used a stale scale value and could end up at Infinity/NaN. It now uses a unit scale.
• ViewCube.colorNeg: the setter colored the positive (labelled) circles instead of the negative ones.

Behavior change

Gizmo now fires pointer:up on button release even while disabled or while the pointer is locked. In those cases no shape is selected.

Manual smoke test

1. Open the gizmos/transform-translate example. Hover the arrows, planes and center sphere where they overlap on screen. Expected: the shape under the cursor highlights and drags along its own axis or plane.
2. In the same example, start dragging an arrow, set gizmo.enabled = false before releasing, release, then set gizmo.enabled = true and move the mouse without pressing a button. Expected: the box does not move.
3. Open gizmos/transform-scale and turn snapping on with an increment of 1. Drag the X arrow once zoomed in and once zoomed out. Expected: the box scale is a whole number both times.
4. Open misc/editor and set viewCube.colorNeg = new Color(1, 0, 1). Expected: only the three unlabelled circles turn magenta, and X/Y/Z keep their axis colors.

Fixes #

Checklist

• I have read the contributing guidelines
• My code follows the project's coding standards
• This PR focuses on a single change

[github-actions]

Build size report

This PR changes the size of the minified bundles.

Bundle	Minified	Gzip	Brotli
playcanvas.min.js	2673.2 KB (+25 B, +0.00%)	693.3 KB (+66 B, +0.01%)	537.6 KB (+10 B, +0.00%)
playcanvas.min.mjs	2669.9 KB (+25 B, +0.00%)	691.9 KB (+7 B, +0.00%)	537.0 KB (+139 B, +0.03%)