H key and toolbar button use hover-or-last-close, so mouse users had no way
to drop a line at an arbitrary price they hadn't hovered. Shift+Click reads
the click's y via candle.coordinateToPrice — direct positional control.
- Plain click stays as native chart interaction (crosshair/drag)
- Only intercepts when shiftKey held; preventDefault to avoid text selection
- Honors the same 10-line cap as the H key / button
- ShortcutsHelp adds "Shift+클릭" entry next to H so it's discoverable
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