feat: support physical dimension units (pt, mm, cm, in) for print/PDF design systems

[SomSamantray]

Summary

Widens the Dimension grammar from px/em/rem to also accept pt, mm, cm, in — the print-native units CSS already supports — so print/PDF-targeting DESIGN.md files (academic papers, book layouts, page.pdf()/WeasyPrint pipelines) can express normative values without lossy conversion.

Closes #162.

What's in here

• Schema (spec-config.yaml): added pt, mm, cm, in to the units: list — the single source of truth re-exported as STANDARD_UNITS. No new print-specific category; per the issue, this is straightforward acceptance, not a new taxonomy.
• De-duplication (model/handler.ts): the rounded and typography (fontSize/lineHeight/letterSpacing) blocks each hand-spelled a unit !== 'px' && unit !== 'rem' && unit !== 'em' literal check that bypassed the config entirely — widening the YAML alone would have updated the docs while the linter kept rejecting the new units. Both sites now check against a STANDARD_UNIT_SET derived from the same config, so there's one source of truth and the next unit addition only touches spec-config.yaml.
• Removed a second duplicate: found while testing — spec-config.yaml's types.Dimension had its own hardcoded units: sub-list, stale and separate from the top-level list. Removed it so the doc renderer's existing fallback (config.STANDARD_UNITS) is the only path.
• Docs: docs/spec.md regenerated via bun run spec:gen (never hand-edited); README's token-type table updated to match.

Review notes

A simplify pass caught a subtlety worth flagging: the first version of the handler.ts fix called the existing isStandardDimension(raw) helper, which re-parses the raw string internally — but both call sites already have the parsed dimension in hand (resolved/parsed) from a parseDimension() call one line earlier. Three independent review lenses (reuse, quality, efficiency) all flagged the same redundant re-parse; fixed by checking the already-parsed .unit against STANDARD_UNIT_SET directly instead.

Testing

• bun test — 315 pass, 0 fail.
• bunx tsc --noEmit clean.
• bun run spec:gen --check confirms deterministic doc generation.
• New tests cover: pt/mm/cm/in acceptance in both rounded and typography, non-standard units (vh) still rejected, and px/em/rem behavior unchanged.

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_{🤖 Assisted by Compound Engineering}