Mouse-only support

[marcosqlbi]

SQLBI Whiteboard currently supports only touchscreens and pen tablets. We didn't want any compromise, so the mouse is a second-class citizen and cannot be used to draw with the pen or highlight.

[marcosqlbi]

Mouse drawing ships in 1.2.0.

Help → Preferences → Input → Mouse drawing turns the left button into whichever tool is selected on the toolbar — Pen, Highlighter, Calligraphy, Eraser, Select, Pan, or the laser. It defaults to on where Windows reports neither a pen tablet nor a touchscreen, and can be set to On or Off explicitly, because what Windows reports is a list of digitizers rather than an answer about what is plugged in.

The rule we settled on is that a mouse gets the tools, not the gestures. Everything on the toolbar becomes reachable, and Eraser and Pan join it as they already do for finger drawing. Nothing that exists because of what a hand and a pen can do is simulated: there is no pressure, so ink is drawn at an even width — Calligraphy is the one tool that still varies, because its width comes from speed — and the rear eraser, hover, and palm rejection still need a pen.

Two things move to Ctrl, because the left button is busy. Ctrl and the left button select, move, and resize a container and hand the drawing tool back, which is what the left button did on its own before; Ctrl with a double-click fits one to the canvas. The tool also stays selected now instead of being handed back after every gesture.

Nothing about the pen path changed, so Mouse drawing can be left on beside a pen.

The reasoning, including the alternatives that were weighed and rejected, is in docs/mouse-mode.md and decision 23 of docs/decisions.md. Downloads are at https://whiteboard.sqlbi.com.