Use native scroll telemetry to make scroll top and bottom more deterministic

## What to build

Improve `scroll top` and `scroll bottom` confidence by using native scroll telemetry when a platform can expose it, such as scroll offset, first visible item, or equivalent accessibility scroll position. This should reduce reliance on visible snapshot signatures for virtualized or homogeneous lists.

The command should remain fast and should not reintroduce blind multi-pass scrolling.

## Acceptance criteria

- [ ] Scroll-edge state can consume a platform-provided scroll position signal when available.
- [ ] If telemetry changes while the visible signature is unchanged, edge scrolling continues instead of treating the list as stuck.
- [ ] If neither signature nor telemetry changes, the command fails with the existing scoped-scroll error semantics.
- [ ] Regression coverage includes a homogeneous or repeated-row list where visible labels stay stable while the list moves.
- [ ] Android, Apple, and fallback behavior remain documented in tests or capability comments where telemetry is unavailable.

## Blocked by

None - can start immediately