Improve desktop touch input and process warnings

[SaicharanKandukuri]

• Adds a draggable mouse palette with left, middle, right, and scroll controls.
• Supports hold-and-drag and latched mouse buttons while keeping the desktop responsive to touch.
• Warns when Android child-process restrictions may stop Linux desktops or apps.
• Links directly to Developer options on supported Android versions.
• Adds focused tests for mouse-button state and process-restriction detection.