Fix spurious ~34px horizontal scroll on csskit.rs (bump taffy)

[nicoburns]

Summary

https://csskit.rs showed a spurious ~34px horizontal scroll at a 1200px viewport. Root cause: taffy's block/grid (and flexbox) algorithms unconditionally added a container's own end-side padding to its content_size, even for boxes that are not scroll containers. The page's footer (a padded block whose child <p> has negative horizontal margins pulling it into the padding) reported content_size.width = 1234, which propagated to the root and made the document scrollable (scroll_width = 34).

Fixed upstream in DioxusLabs/taffy#1114: end-side padding is now only included in content_size when the container is a scroll container, matching browser scrollable-overflow semantics. This PR bumps the taffy rev to pick that up (the pinned rev is the fix commit on the PR branch; can be re-pinned once the taffy PR merges), and adapts to taffy's LayoutOutput::first_baselines → baselines: Baselines rename that landed on taffy main in between:

// packages/blitz-dom/src/layout/{mod,inline}.rs
- first_baselines: Point { x: None, y: first_baseline },
+ baselines: taffy::Baselines::from_first(first_baseline),

Verified with the screenshot example: the csskit.rs root goes from content_size=1234x3246, scroll_width=34 to content_size=1200x3246, scroll_width=0, with rendering unchanged. cargo test --workspace, clippy and fmt pass.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/b6f5529e9a3e4823b603788b475ab109
Requested by: @nicoburns

WPT results

No changes in test results compared to main.

_{Generated by the WPT workflow.}

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