[codex] Reset drag direction between drags

[nexiumbiz-debug]

Summary

• reset the draggable lastMouse baseline when a new drag starts so direction checks do not reuse the previous drag's pointer position
• clear the baseline again when drag stops
• add a regression spec showing a second drag starts from the current pointer and correctly treats movement away from the right edge as LEFT

Addresses the stale lastMouse part of #854.

Tests

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

[tiberiuzuld]

this should reset to 0, since getDirections needs to set current position of mouse from dragMove mouse event.