墨痕归卷，字库随行 · Bundle CJK fallback fonts for PDFium

[eric8810]

Summary

• bundle the checksum-pinned official Noto Sans SC regional subset and its OFL license in every native npm platform package
• rebuild the exact reviewed pdfium-native 0.6.1 addon so PDFium initializes from the package-local font directory
• add a deterministic non-embedded STSong-Light fixture that gates font selection, rendered PNG content, and end-to-end Chinese OCR
• advance the immutable release closure to Core/native 0.5.6, runtime 0.1.6, Document 0.1.2, and Tiny/Medium 0.1.5

Why

The 0.5.5 packages include PDFium but no fallback fonts. A PDF that references a Chinese font without embedding glyphs can therefore become blank or tofu-like during rendering before OCR sees the page. This change closes that renderer dependency inside npm and keeps install/runtime free of secondary downloads.

The official SC regional subset preserves the tested fallback behavior while reducing the per-platform font payload from 16.44 MB to 8.33 MB unpacked and from about 13.59 MB to 7.20 MB in the npm tarball.

Validation

• macOS arm64 real PDFium render: STSong-Light -> Noto Sans SC, non-empty PNG
• end-to-end default model OCR: 中文测试
• Unicode installation-path loader smoke
• 17 Python release/patch/CI contract tests
• all workspace Node tests
• strict TypeScript typecheck
• git diff --check

Six-platform package smoke remains the required CI evidence before release.