Bump Taffy to fix default block alignment safety

[nicoburns]

Summary

Pin Taffy to DioxusLabs/taffy#1288, making compute_block_align_content_offset default to safe overflow alignment while preserving explicit unsafe. This covers Taffy's block layout and callers laying out line boxes externally; Flexbox/Grid defaults are unchanged.

Preserve explicit unsafe in stylo_taffy::convert::content_alignment: previously it was discarded, relying on Taffy's default being unsafe. Changing the default exposed seven WPT regressions. Add a conversion regression test covering default, safe, and unsafe end/center/flex-end for block, inline-block, table-cell, flex, and grid displays.

Full CSS+SVG WPT CI now matches main: all seven regressions are restored, with no new passes or failures. Blitz already supplies safe defaults for block containers. The original pin's table-cell gain also disappears, since it depended on losing explicit unsafe; that subtest remains an existing failure, requiring a table-cell-specific fix.

Formatting, workspace check and Clippy, and blitz-dom/stylo_taffy/blitz-tests tests pass. The full release local WPT A/B (36,274 tests) also has no regressions relative to main.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/3c766f9ec5f343c3b0c65e447a5ca7a6
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/3c766f9ec5f343c3b0c65e447a5ca7a6?variant=devin-insiders
Requested by: @nicoburns

WPT results

No changes in test results compared to main.

_{Generated by the WPT workflow.}

[staging-devin-ai-integration]

I'll fix CI failures and address comments from users with write access that start with 'Devin'.

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