feat: render project fonts in editor

[nighca]

Depends on #3362.
Closes #3366.

Summary

• provide project fonts and the fontPreferences array to the editor SVG rendering context;
• apply project font semantics to SVG font-family references;
• rasterize SVG image previews from project font buffers through Resvg/WASM;
• update image-preview consumers to use the font-aware rendering path.

Status

This PR remains draft and must not merge yet.

• The WASM approach avoids the large-font data-URI performance problem, but current usvg 0.47 fallback merges glyphs by index rather than grapheme cluster.
• It therefore fails valid project-font cases: a variation selector or ZWJ emoji earlier in a text run can prevent a later basic-chinese fallback, and compound emoji do not render as atomic fallback clusters.
• Upstream linebender/resvg#1087 implements the required cluster-boundary merge, but is open and unreviewed. See the tracking issue's POC status for the detailed reproduction and decision options.

[gemini-code-assist]

Caution

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