[FEATURE] Add i18n (internationalization) support

[0xliam627]

Description

Add multi-language support to EndGit web dashboard. The platform should be accessible to non-English speaking users, especially in the Endstone community which has a significant presence in Asia.

Proposed languages (initial)

• English (default)
• Vietnamese
• Chinese (Simplified)
• Korean
• Russian

Tasks

• Set up translation file structure (/messages/en.json, /messages/vi.json, etc.)
• Add language switcher component to navbar
• Extract all hardcoded strings from existing pages
• Implement locale detection (browser preference / user setting)
• Add cookie-based
• Translate core pages: home, plugins, builds, FAQ, rules, terms

Notes

• Cookie/header-based locale
• Consider storing user language preference in the database
• SEO: each locale should have proper hreflang tags