0.34.0 — Token-as-API contract guardrail; opt-in autoMigrate

Added

• Token names are now a versioned API contract, with a guardrail. Each
  tokens.css migration declares kind: 'additive' | 'breaking'. A new
  check:token-contract (wired into prepublishOnly, plus
  tokensCssMigrations/contract.test.ts) verifies behaviorally that an additive
  migration never removes or renames a token (catches a breaking change shipped
  as backward-compatible), and gates breaking migrations on a major bump from
  1.0.0 (pre-1.0 it warns). See TOKENS.md and RELEASING.md.
• themeFileApi({ autoMigrate: true }). Opt-in: the dev server applies
  pending additive token migrations to your tokens.css at startup and
  writes the file (shown in git), so it stays current with the package without a
  manual step. Breaking migrations are never auto-applied. Off by default, which
  preserves the invariant that the plugin never writes tokensCssPath unless you
  enable it.

Docs

• TOKENS.md gained a plain-language section on how token changes are
  versioned (additive vs breaking, what an upgrade can and cannot change).