fix: restore Windows UI Automation elements

[dttxorg]

What changed

• Materialize the Windows UI Automation Generic.List[object] with .ToArray() before returning it from PowerShell.
• Keep virtual/offscreen UIA elements while omitting non-finite pixel bounds, so Infinity never corrupts the JSON transport.
• Absorb the native runner's late asynchronous stdin EPIPE and defer to the authoritative helper close/result.
• Add source regressions, Windows PowerShell 5.1 smoke coverage, and a real Windows window-observation assertion requiring a non-empty UIA tree.
• Prepare patch release 0.5.9.

Root cause

Windows PowerShell 5.1 throws System.ArgumentException: Argument types do not match when @(...) directly wraps this generic list. The helper's catch converted that exception into an empty element array, so every semantic Windows observation returned elementTotal: 0.

Once the list was correctly returned, CI also exposed UIA's non-finite virtual bounds: PowerShell serialized those as a bare Infinity token. The helper now preserves the semantic element and omits only unusable bounds.

Validation

• Issue-specific baseline reproduces the old empty-tree path.
• UIA non-finite geometry baseline reproduces the invalid-JSON path.
• Native runner late-EPIPE regression: 30 consecutive targeted runs passed.
• npm run check: 112 passed.
• npm run pack:dry: package 0.5.9 generated successfully.
• Rollback rehearsals restore the original SHA-256 and original failing behavior.
• GitHub Actions CI run 32221093731: Ubuntu, macOS, and Windows all passed.
• Windows PowerShell 5.1 parse/list-materialization and native desktop observation all passed.

Fixes #1