refactor(web-ui): govern exception palette readiness

[limityan]

Summary

• Add colorDomainNearPairs.* reporting and baseline budgets for specialized theme color domains while keeping ordinary component/app near-pair debt at 0.
• Add generated widget payload externalOnlyCompatibility metrics so legacy iframe payload keys are visible as a compatibility queue instead of internal usage debt.
• Reduce repeated theme preset git palette literals with createGitColors, preserving explicit overrides where staged and added colors are semantically different.
• Harden the color audit against local build order by ignoring generated version artifacts and reporting ignoredGeneratedFiles separately from test exclusions.
• Update the theme token optimization document with the refreshed baseline, specialized near-pair queue, and remaining governance boundaries.

Risk and review notes

• No intentional UI visual change. The preset output hash test keeps resolved built-in theme objects stable, and Tokyo Night keeps its explicit staged color because it differs from added.
• Specialized near-pair metrics are an evidence queue, not an automatic merge rule. App UI remains guarded separately by ordinary nearPairs.* and domain-level appUi zero budgets.
• Generated widget legacy keys are still exported for compatibility. This PR only classifies the external-only compatibility surface and prevents undefined or missing-canonical payload keys.
• Local build:web generates ignored src/web-ui/src/generated/version* files; the audit now excludes those build artifacts so clean-source and post-build audit runs keep the same production color counts.

Validation

• pnpm run theme:color-audit
• pnpm run theme:color-audit:test
• build-artifact order check: after generate-version/build:web, theme:color-audit -- --json keeps filesScanned=1535, colorOccurrences=1702, appUi=0, nearPairs.nearTotal=0
• pnpm --dir src/web-ui run test:run src/infrastructure/theme/presets/themePresetOutput.test.ts
• pnpm run theme:visual-contract
• pnpm run lint:web
• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run
• pnpm run build:web
• git diff --check