refactor: extract patterns.ts and placeholder-replacer.ts from index.ts

[Wolfvin]

Summary

Refactors the monolithic src/shared/index.ts (498 lines) into three well-structured modules with clear separation of concerns, while preserving 100% identical behavior.

What Changed

Extracted Modules

• src/shared/patterns.ts — All 60+ regex patterns and character class constants (CJK, AN, operators, brackets, quotes, file paths, etc.)
• src/shared/placeholder-replacer.ts — PlaceholderReplacer class for protecting content during regex processing

Decomposed spacingText() into Private Methods

Method	Responsibility
applyPunctuationSpacing()	Dots, periods, colons, tildes, commas, semicolons
applyQuoteSpacing()	Double, single, curly quotes, possessives
applyHashSpacing()	Hashtag/hash spacing with slash context awareness
applyOperatorSpacing()	Arithmetic operators (+, -, *, =, &)
applyComparisonOperatorSpacing()	Comparison operators (<, >)
applyFilePathSpacing()	Unix/Windows file path spacing
applySlashSpacing()	Context-aware slash handling (operator vs separator)
applyBracketSpacing()	Bracket spacing around CJK text
fixBracketInnerSpacing()	Inner bracket content cleanup

Regression Proof

This refactoring was validated using output-based regression testing (the Regrets skill) with a 3-layer verification:

Verification 1 — Regrets Fingerprints

All 8 behavioral clusters remained GREEN across 5-run drift tests.

Cluster	Fingerprint	Status
cjk-alphanum-spacing	n30nmvg	✅ STABLE
cjk-symbol-spacing	4a14yk9	✅ STABLE
cjk-punctuation-spacing	1fwk5dr	✅ STABLE
cjk-slash-path-spacing	2nj1rhd	✅ STABLE
cjk-quote-bracket-spacing	59cgutn	✅ STABLE
cjk-grade-compound-spacing	41cod4b	✅ STABLE
cjk-html-tag-spacing	1usarqr	✅ STABLE
has-proper-spacing	4r4g9yv	✅ STABLE

Verification 2 — Direct Output Match

All 57 test cases produce output identical to the pre-refactor ground truth (KEBENARAN 1).

Verification 3 — Fingerprint Cross-Check

All 8 regenerated fingerprints match the pre-refactor fingerprint contract (KEBENARAN 2).

Existing Tests

All existing vitest test suites (30 test files, 60+ test cases) continue to pass.

Why This Refactoring?

1. Readability: The 498-line index.ts was a monolith mixing pattern definitions, utility classes, and spacing logic
2. Maintainability: Each concern now has its own file with clear imports
3. Discoverability: New contributors can find relevant patterns in patterns.ts without scrolling through 500 lines
4. Testability: Individual spacing steps can be understood and reasoned about independently