Resolve authored theme token overrides

[artiphishle]

Summary

ADM-13 Surface owner phase for canonical authored theme tokens from @ankhorage/contracts.

This PR:

• updates Surface to consume @ankhorage/contracts@^7.2.0
• resolves canonical ThemeConfig.tokens overrides into runtime spacing, radii, typography and shadow tokens
• preserves Surface defaults for omitted authored values
• validates invalid numeric, heading and font-weight values explicitly
• keeps reserved zero tokens canonical
• keeps module-derived font-family state out of persisted theme source
• fixes nested default-token mutation so one resolved font theme cannot leak into later themes
• adds focused merge/inheritance, validation and font-isolation regression tests
• refreshes generated Paradox documentation deterministically with @ankhorage/paradox@^0.1.21

Token policy

• spacing, radii, typography size and shadow families may accept authored extension token names
• typography weight slots remain the canonical Surface slots
• heading slots remain canonical levels
• numeric tokens must be finite and non-negative; typography dimensions must be positive
• spacing.none and radii.none remain zero

Validation

Dedicated ADM-13 refresh gate:

• install / lock refresh
• build
• lint
• format check
• Knip
• 125 tests
• typecheck
• Paradox docs generation
• explicit generated-doc guard for /home/runner/ and /Users/
• changeset status

Generated artifacts were then formatted with the repository's canonical Prettier configuration. Both temporary helper workflows removed themselves and are absent from the final diff.

Final normal PR CI on head 48868d3951e21bd69595c110c13186fb053a5feb passes frozen install, build, lint, format check, Knip, tests, typecheck and changeset validation.

Release

Minor release: @ankhorage/surface@2.2.0.

Downstream ZORA/Studio work must wait for this Surface release; no downstream compatibility workaround belongs in this PR.