Introduce the pure preference layer and the framework-wide value port that the
runtime layers (`arts/prefs`, format, frontend) consume.
- `libs/reactive` gains `Source<T>` — a small `{ get, onChange? }` port any
artifact uses to observe an external value (locale, currency, theme, …).
- `libs/locale` extracts the lookup-style `matchLocale` helper plus aliases
`LocaleSource` to `Source<string>`. Tests added for the four-step
exact / lang+script / lang+region / lang priority.
- New per-domain libs (`currency`, `density`, `direction`, `motion`, `theme`,
`timezone`, `units`) own their own primitives, capability sources and pure
helpers (`*FromLocale(s)`, `directionFromLanguage`, `resolveTheme`,
`resolveMotion`). The currency catalogue + region table moved here from
`arts/format/currency`.
- `libs/prefs` is the pure preference layer: `PrefsCapabilities`,
`PrefsEnvironment`, `PrefsIntent`, `PrefsEffective`, intent validation
(with stable `PrefsValidationFailure` codes) and the parallel-projection
resolver. Each `effective` field is now an INDEPENDENT projection of
`environment.locales[]` against its own capability catalog — `language`
and `locale` are split (i18n catalog vs regional formatting); `currency`,
`unitSystem`, `direction` derive per-dimension instead of from a single
`effective.locale` anchor.
- `arts/format` and `arts/frontend` migrated to the new `Source<T>` shape:
`localeSource?.getLocale()` → `localeSource?.get()` and
`onLocaleChange?` → `onChange?`. `arts/format/currency/locale-currencies`
and `arts/format/units/locale-defaults` collapse to thin re-exports of
their `libs/*` counterparts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
