feat: adopt Nebula Sans across Atet surfaces

[0thernet]

Summary

• adopt the canonical Nebula Sans v0.2.1 payload for the Atet website, inert preview, desktop recorder, and Direct workbench while preserving the serif hero and explicit mono/custom roles
• make default diagram SVG and PNG output deterministic with checked Book/Bold font assets, and rasterize only owned caption sprites through Resvg without repeating font payload per cue
• regenerate the social image from checked sources and fonts, allow only self-hosted fonts in both site CSPs, and retain Site Footer v0.3.0 plus current rich-label behavior
• ship the font assets through standalone SDK and desktop packages with license, provenance, cache identity, and installed-consumer coverage

Verification

• bun run check
  • SDK: 208 pass, 0 fail
  • desktop: 1,215 pass, 16 intentional skips, 0 fail
  • web: 30 pass, 0 fail, deterministic build
  • standalone boundary and installed-package consumer smoke: pass

[vercel]

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Project	Deployment	Actions	Updated (UTC)
atet	Ready	Preview	Aug 27, 2026 9:08pm