feat(font-system): bundle TeX Gyre Bonum fallback

[caio-pizzol]

Bundles TeX Gyre Bonum so Bookman Old Style can resolve to the reviewed DocFonts fallback once the stacked OFL batch lands. This is isolated because it adds the GUST Font License surface and the four Bonum faces.

Why:

• Bookman Old Style is a visually accepted fallback in DocFonts.
• All four Bonum faces are real faces, so no synthetic face handling is needed for this row.
• The asset-gate test now proves the gate directly by denying this bundled family through canRenderFamily.

Verified:

• pnpm --filter @superdoc/font-system test src/substitution-evidence.test.ts
• pnpm --filter @superdoc/super-editor test src/ui/react/hooks.test.tsx
• pnpm check:font-licenses
• pnpm --filter @superdoc/font-system typecheck
• pnpm --filter @superdoc/font-system build

Stacked on caio-pizzol/docfonts-ofl-batch-3.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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