Fix Dataframe select event firing twice on click

[gambletan]

Summary

Fixes #12054 — The Dataframe .select() event handler fires twice for a single click.

Root cause: In js/dataframe/shared/utils/drag_utils.ts, the handle_cell_click function (which dispatches the select event) was called twice:

1. In start_drag (on mousedown) — correctly selects the cell and dispatches select
2. In end_drag (on mouseup) — redundantly calls handle_cell_click again when no drag occurred (!state.is_dragging && state.drag_start)

Fix: Remove the redundant handle_cell_click call from end_drag. The start_drag handler already handles cell selection and event dispatch for simple (non-drag) clicks. The end_drag handler only needs to clean up drag state and restore focus when an actual drag operation ends.

This explains the behavior reported in the issue — a "hold click" (mousedown, wait, mouseup) fires the select event on both mousedown and mouseup, while a quick click may appear to fire once due to debouncing or timing.

Test plan

• Click a cell in a non-interactive Dataframe — select event should fire exactly once
• Hold-click a cell (mousedown, wait ~1s, mouseup) — select event should fire exactly once
• Drag across multiple cells — selection should still work correctly
• Shift-click / Ctrl-click multi-select should still work
• Verify with the reproduction script from the issue

🤖 Generated with Claude Code

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