fix(layout): recover mixed-case tracked words

[yzxcj797]

Summary

• Fixes Corrupted text extraction for text-based PDFs #211.
• Detect a conservative bimodal signature for mixed-case glyph-per-item tracking and rejoin each title-case word while retaining real word gaps.
• Keep deliberately spaced lowercase single-letter sequences unchanged, alongside the existing all-caps and spaceless-CJK handling.

Testing

• cargo test --target x86_64-pc-windows-gnu
• cargo clippy --target x86_64-pc-windows-gnu -- -D warnings
• cargo fmt --all -- --check
• git diff --check

---

Summary by cubic

Recover mixed-case glyph-per-letter tracking into words while preserving real word gaps. Previously, mixed-case runs (e.g., JohnDoe) split into 1–2 character fragments; now a conservative bimodal gap detector rejoins title-case words without changing lowercase spaced singles or existing all-caps/CJK behavior. Fixes #211.

• Introduces a shared gap-splitting helper (largest_relative_gap_jump) and routes non-CJK, non-all-caps runs through a title-case path that requires a strong jump and at least two ≥3-letter title-case words before merging.
• Keeps lowercase single-letter sequences unchanged; preserves existing all-caps and spaceless CJK handling.
• Adds unit and integration tests, including a synthetic PDF with custom font metrics to reproduce resume-style tracking; no API or option changes.

^{Written for commit 87bd26d. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 2 files

<sub>Shadow auto-approve: would not auto-approve because issues were found.

Fix all with cubic | Re-trigger cubic</sub>

[cubic-dev-ai]

0 issues found across 1 file (changes from recent commits).

<sub>Shadow auto-approve: would auto-approve. Introduces a conservative heuristic to rejoin mixed-case tracked words (e.g., JohnDoe) while preserving lowercase spaced single-letter sequences and existing all-caps/CJK handling. The fix is focused, test-driven, and does not change any API or operational configuration.

Re-trigger cubic</sub>