[Integration] useLocale system composable integration

[johnleider]

Summary

Integrate useLocale with the v0 plugin system for unified configuration and cross-composable awareness.

Integration Points

• Accept configuration from unified v0 plugin options
• Provide locale to useDate for locale-aware formatting
• Persist locale preference via useStorage
• RTL detection for useTheme CSS variable injection

Related

• [Audit] useLocale - ensure parity with Vuetify createLocale #105 - Audit useLocale parity with Vuetify
• [Integration] Convert Vuetify to use @vuetify/0 useLocale #110 - Convert Vuetify to use v0 useLocale