devex: migrate to vue-i18n

[Prospector]

This pull request migrates the frontend internationalization (i18n) system from the deprecated @vintl/vintl library to a new stack based on vue-i18n and the i18n utilities provided by @modrinth/ui.

• Replaces @vintl/vintl with vue-i18n and intl-messageformat, and replaces all usage of @vintl/vintl across the codebase with composable wrapper from @modrinth/ui
• Refactors all component and module imports to use i18n helpers (defineMessage, defineMessages, useVIntl, etc.) from @modrinth/ui instead of @vintl/vintl, and updates related type imports.

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• Languages must be manually added - I think enabling languages when they hit the 80% complete threshold on Crowdin is probably the best idea here.
• Decided not to rename the final i18n composable away from useVIntl as it was easier to migrate.