Add vsc-unicode-natural sort order (VS Code / Windows Explorer style)

[siakun]

Summary

Adds a new sort order token vsc-unicode-natural (alias: unicode-charcode-natural) that combines the existing vsc-unicode ordering with numeric-aware digit-run comparison. This mimics the default file sort behavior of VS Code and Windows Explorer.

Motivation

Users whose system locale is non-Latin (e.g. ko-KR, ja-JP) currently face a gap between the two closest existing options:

Option	Latin before CJK?	Natural number sort?
< a-z	❌ CJK-first in many locales	✅
< vsc-unicode	✅	❌ Part 10 < Part 2
< vsc-unicode-natural (new)	✅	✅

Concrete example from a Korean-locale vault with a book folder containing Part 0 through Part 8, 부록 A, 부록 B, 부록 C:

• With < a-z → 부록 A, 부록 B, 부록 C, Part 0, ... (CJK first)
• With < vsc-unicode → Part 0, ..., Part 8, 부록 A, ... (ok for now) but Part 10 would sort before Part 2
• With < vsc-unicode-natural → correct Windows/VSCode order, scales to Part 10+

Implementation

Uses + 'Intl.Collator' + (' + 'en'+, { numeric: true, sensitivity: 'base' })`:

• Fixed en locale so collation is consistent across user machines; CJK stays after Latin via UCA defaults
• numeric: true enables natural digit-run comparison
• sensitivity: 'base' matches the existing alphabetical comparator's case/accent-insensitivity
• Punctuation/symbols precede letters via UCA weights, so [TODO] correctly sorts before CLAUDE (matches VS Code behavior)
• Uses sortStringWithExt so files with identical basenames but different suffixes (e.g. + 'name (variant).md' + vs + 'name.md' + ) sort the way VS Code orders them

Changes

• CustomSortOrder enum: add vscUnicodeNatural / vscUnicodeNaturalReverse
• custom-sort.ts: add CollatorCompareVscNatural and two Sorters entries
• sorting-spec-processor.ts: register vsc-unicode-natural and unicode-charcode-natural tokens. Important: these are placed before the existing vsc-unicode / unicode-charcode entries because the parser uses a startsWith match on Object.keys(OrderLiterals) in declaration order, otherwise vsc-unicode-natural is partially matched as vsc-unicode with -natural as trailing garbage
• sorting-spec-processor.spec.ts: add a parser recognition test that parallels the existing vsc-unicode coverage

Tests

All 831 existing tests pass, plus the new test for vsc-unicode-natural / unicode-charcode-natural token recognition.

Example usage

---
sorting-spec: |-
  target-folder: /*
  /folders
    < vsc-unicode-natural
  /:files
    < vsc-unicode-natural
---

Notes

• No changes to manifest.json, package.json, or versions.json since those are release-time concerns
• Backward compatible: existing sortspecs using < vsc-unicode or < a-z continue to work unchanged
• Happy to adjust token naming (e.g. vsc-unicode-numeric), add more tests, or split into smaller PRs if preferred