Connect locale state to semantic bidi boundaries

[smiggleworth]

Summary

Milestone 1 — direction contract

• resolve locale direction with Intl.Locale#getTextInfo(), a likely-script compatibility fallback, and explicit application overrides
• default locale scopes such as Arabic to RTL while retaining runtime validation
• expose frozen, typed semantic { lang, dir } attributes

Milestone 2 — explicit DOM integration

• expose localeAttributes() for SSR templates and client locale selection
• expose applyLocaleAttributes() for an explicit DOM target without hidden global mutation
• expose i18n.attributes() for real nested language/direction boundaries

Milestone 3 — production-faithful verification and guidance

• run Chromium contract tests for atomic document switches, nested opposing boundaries, bdi, dir="auto" inputs, logical spacing, and overlay anchoring
• document SSR-before-hydration application, nested scopes, unknown-direction content, and logical CSS
• keep the browser contract in the default npm test / npm run check gate

Verification

• npm run check
• npm run fmt -- --check
• git diff --check
• 23 unit/package tests and 5 Chromium browser tests

Closes #23

No package version was changed and no package was published.

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