fix(drawbox): start freehand strokes at the exact press point

[akshay2211]

PEN/shape/eraser drags were driven by detectDragGestures, whose onDragStart only fires after the pointer crosses the ~8dp system touch slop and reports the slop-crossing position — so strokes began offset from and slightly after the finger-down point.

Replace it with a custom awaitEachGesture loop that begins drawing-mode gestures on the first movement with zero touch slop, seeded at the true press point, while keeping the system slop for SELECT/PAN so a click isn't misread as a drag. Starting on first move (not on down) keeps the tap handler as the sole handler for taps and avoids stray dots when a pinch begins before any drag.

Summary

Type of change

• Bug fix (non-breaking)
• New feature (non-breaking, additive to the frozen 2.x surface)
• Incubating API (opt-in via annotation)
• Breaking change (would land in a future major)
• Docs / build / CI only

Affected targets

• Android
• iOS
• JVM Desktop
• Web (WASM)
• Web (Kotlin/JS)

Public API impact

• No public API change
• Additive only (new symbols, no signature changes)
• Modifies a 2.x frozen surface — link to RFC or discussion:

Testing

• Unit tests added / updated
• Snapshot tests updated (Roborazzi baselines regenerated if applicable)
• Manually verified on:

Checks

• ./gradlew :DrawBox:spotlessCheck passes
• ./gradlew :DrawBox:jvmTest passes
• ./gradlew :DrawBox:dokkaGenerateHtml passes
• CHANGELOG entry added under the correct release heading (if user-facing)
• Migration notes added (if the JSON scene format or a frozen surface moved)

Screenshots / recording

Linked issues