Fix wrapped UI text auto height

[kkkiio]

Summary

• Share the existing wrap and truncation helpers between Taffy leaf measurement and UI rendering.
• Measure automatic text height from prepared lines using the logical content width, including padding and border insets.

The leaf measure callback previously measured the full string as one line and ignored TextLayout. Rendering then wrapped against the final content rect, so Taffy could record a 16px height while two 16px lines were drawn. The change keeps the existing text helpers in place and adds prepare_text_layout as the shared orchestration layer. Taffy per-tree leaf measurement caching remains unchanged; no persistent cache is added.

Fixes #48

Checks

• moon check src/ui --target all --deny-warn
• moon test src/ui --target native --release --deny-warn

[Milky2018]

Thanks for the contribution. This was merged with an additional end-to-end regression covering the final computed node height, not only the leaf measurement helper. UI tests pass on the current Chicle backend, and the fix is available in Selene 0.37.0.