Fix touch panning when drag selection is enabled - #5918

Summary

• let the existing touch-pan gesture win over pane selection capture when drag panning is enabled
• preserve explicit selection-key behavior and primary-mouse marquee selection
• keep React and Svelte behavior in sync
• clarify that panOnDrag button arrays restrict mouse input, not touch input

Why

When selectionOnDrag is enabled and panOnDrag is a mouse-button array such as [1, 2], a primary touch currently starts both viewport panning and a marquee selection. The system filter intentionally treats button arrays as mouse-only for touch panning (see #4229), so the Pane should not capture the same touch as a selection unless the selection key is explicitly active.

This uses the gesture's actual pointerType, so hybrid touchscreen computers keep normal mouse and pen behavior.

Behavior

• touch + enabled panOnDrag + no selection key: pan without marquee
• touch + selection key: marquee selection
• primary mouse button excluded from panOnDrag: marquee selection
• panOnDrag={false} and pen behavior remain unchanged

Tests

• added a desktop-profile, touch-enabled Playwright regression for the conflict
• verified the regression fails on the pre-fix code with one unexpected selection marquee
• added coverage for selection-key touch behavior and primary-mouse behavior
• React pane suite: 29 passed, 4 skipped
• Svelte pane suite: 29 passed, 4 skipped
• React and Svelte package typechecks, builds, and changed-file lint/format checks pass

Related to #2709.