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fix(virtual-list): prevent scroll flash on variable-height item expand (#339)

* build: update dependencies

- Bump @typescript-eslint/eslint-plugin to ^8.56.0
- Bump @typescript-eslint/parser to ^8.56.0
- Bump typescript-eslint to ^8.56.0
- Bump @playwright/test to ^1.58.2
- Add @playwright/cli dev dependency

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* style(docs): normalize quote style in examples page

Standardize string quotes in examples metadata object
to match project formatting conventions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(virtual-list): prevent scroll flash from single-item height outliers

When scrolled deep into a variable-height list, expanding an accordion
item not yet in the height cache would set its height (e.g. 117px) as
the global itemHeight estimate. With _measuredCount === 0 in the browser
path, _totalHeight = _itemLength × _itemHeight caused totalHeight to
spike from ~49,000 to 117,000px — a visible flash/fly-up.

Fix: skip heightManager.itemHeight update when newValidCount === 1,
preventing single-item outlier measurements from swinging the estimate.

Also set overflow-anchor: none permanently on the viewport element to
prevent browser scroll anchoring from interfering with the virtual
list's own scroll correction logic, and update ReactiveListManager to
keep overflow-anchor as 'none' throughout dynamic updates.

Fixes #327

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

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