Description & Design

This PR adds an initial internationalization foundation for the Maintainerr UI.

It introduces:

• A lightweight UI i18n provider based on the existing settings.locale
• English and Spanish JSON locale files
• Translation keys for selected navigation, settings, rules, and collections UI text
• A short README describing a Weblate/Crowdin-friendly translation setup

The goal is not to translate the whole application in one PR, but to establish a simple structure that can be expanded incrementally and connected to a community translation platform later.

Related issue

No related issue.

AI-Assisted Development

This PR was prepared with AI assistance from Codex.

AI assistance was used to:

• Inspect the existing UI structure
• Scaffold the initial i18n provider
• Extract a first small set of visible UI strings
• Run local validation commands

I reviewed the resulting diff and validation output before submitting. The implementation is intentionally small and avoids adding a new runtime dependency.

Checklist

• I have read the CONTRIBUTING.md document.
• I understand the code I am submitting and can explain how it works
• I have performed a self-review of my code
• I have linted and formatted my code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

How to test

Validated locally with:

1. node .yarn/releases/yarn-4.11.0.cjs --cwd packages/contracts build
2. node .yarn/releases/yarn-4.11.0.cjs --cwd apps/ui lint
3. node .yarn/releases/yarn-4.11.0.cjs --cwd apps/ui check-types
4. node .yarn/releases/yarn-4.11.0.cjs --cwd apps/ui build
5. node .yarn/releases/yarn-4.11.0.cjs --cwd apps/ui test

Additional context

The locale files are stored as JSON under apps/ui/src/i18n/locales/, which should be compatible with Weblate or Crowdin-style community translation workflows.