docs: update reorganize-long-files spec to include CSS reorganization
Add Phase 2 (CSS Reorganization) covering:
- Restore styles/ directory (tokens, global, utilities, syntax-highlight)
- Restore styles/pages/*.css for page-specific styles
- Restore 11 component CSS modules from monolithic styles.css
- Delete styles.css after extraction
Shift frontend page extraction phases to 3-7.
Add visual regression checks to integration phase.
Quality gates unchanged: tsc, build, py_compile, file size limits
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