Add selection property controls and expand toolbar palette

[devmobasa]

The selection properties panel now exposes direct controls for editing selected shapes: palette swatches and a full color picker, numeric steppers, switches, arrow-head segments, drawn arrow styles, and a lock toggle. Pointer activation requires a matching press and release, and wheel input adjusts the hovered row. Short surfaces omit keyboard hints and flow rows into columns. The toolbar also exposes up to 12 palette colors, including the full built-in palette when width allows.

Validation:

• Full local CI reported passing: 4,989 tests with all features and 4,820 without default features.
• Independently rerun during review: 99 properties tests and 647 toolbar tests passed; one toolbar test ignored.
• Whitespace checks passed. Headless checks exercised the real layout and input paths; live Wayland/GTK interaction has not been checked.

Remaining review findings (draft):

• Palette cycling still matches RGB without opacity. With opaque red, translucent red, then green, repeated Right presses get stuck on translucent red.
• Column layout considers height without constraining total width. At 480×360, the mixed-selection panel extends to x=560, leaving the lock and some second-column controls off-screen.