[codex] fix fixed-grid edge auto-scroll

[nexiumbiz-debug]

Summary

• Fixes Grid type "fixed": Moving and resizing the bottom-most panel is very difficult #979 by preventing vertical edge auto-scroll from starting when the pointer is moving away from that edge.
• Also covers Continuous resizing item when placed on the edge without moving mouse #784 by applying the same guard to horizontal edge auto-scroll so right-edge resizing does not keep shrinking when the pointer stops or moves away.
• Keeps existing auto-scroll behavior when dragging/resizing toward the active edge.
• Adds regression coverage for vertical and horizontal scroll-direction guards.

Why

In gridType: "fixed", an item near a grid edge can remain inside the scroll-sensitivity zone while the user drags or resizes away from that edge. The old logic could keep edge auto-scroll running from that zone even though the pointer was no longer moving toward the edge, which made bottom or right-edge items slide or shrink too abruptly.

Checks

• npm run test-lib -- --watch=false
• npm run build-lib
• npx eslint projects/angular-gridster2/src/lib/gridsterScroll.ts projects/angular-gridster2/src/lib/tests/gridsterScroll.spec.ts