Fix long transcript list rendering

[predict-woo]

Summary

• replace the transcript LazyVStack with the native virtualized List
• preserve the intended 16-point row inset
• snap split pane edges to the Retina pixel grid so the native list stays sharp

Closes #7.

Verification

• swift format lint --strict passed
• swift build --package-path Packages/SimbiKit passed
• swift test --package-path Packages/SimbiKit passed all 309 tests
• Xcode Debug build passed
• launched the built app and verified a 336-cue transcript
• confirmed the list host frame moved from x = -0.1, width = 299.1 to x = 0, width = 299