fix: make dragged pieces follow the pointer

[i0ivi0i]

Summary

• move the visible piece shape with mouse or touch pointer coordinates
• preserve board-cell preview and drop behavior while dragging
• add an end-to-end regression test for visual pointer following and placement

Test plan

• pnpm check
• pnpm test
• targeted drag E2E test
• pnpm build
• full pnpm e2e (8/9 pass; existing upstream assertion expects a trailing period that current rankingDescription no longer contains)

Visual verification

The regression test moves a tray piece to board cell 3,3 and verifies that its rendered center stays within 12px of the pointer before drop.