bug: preserve crayon texture for finger input on iOS and Android

[markm39]

Goal

Crayon strokes drawn with a finger should retain the intended crayon texture on both iOS and Android instead of looking smooth or flat.

Context

Crayon drawing with finger input does not appear to get the intended texture. This is not Android-only: without richer stylus/Pencil-style input data such as pressure, tilt, altitude, or azimuth, the current crayon texture path may not have enough signal to drive the same textured output.

Constraints

• Keep iOS and Android behavior aligned.
• Keep stylus and Apple Pencil behavior correct; do not degrade rich-input texture to fix finger input.
• Make the fallback explicit so finger, stylus, and missing-data paths are understandable and testable.
• Avoid a purely random visual workaround that makes strokes unstable between renders or replays.

Done when

• Finger-drawn crayon strokes on iOS and Android show intentional crayon texture rather than a smooth line.
• Stylus/Pencil-drawn crayon strokes still use richer input data when it is available.
• Saved and replayed strokes preserve the same visual texture behavior.
• The example app can be used to compare finger and stylus/Pencil crayon output across platforms.