feat(i18n): Add Spanish (es-MX) locale support

[ellaguno]

Feature Request

Description

Add complete Spanish (Mexican Spanish, es-MX) locale support for the OpenMAIC platform, including:

1. UI translations — All user-facing strings translated to Spanish across all 5 i18n modules (common, stage, chat, generation, settings)
2. Language selector — Spanish option added to the header language picker
3. Browser auto-detection — Automatic detection of Spanish-speaking browsers
4. Content generation — Support for generating courses in Spanish (es-MX added to generation pipeline types)

Motivation

OpenMAIC is a powerful educational platform, and adding Spanish support would make it accessible to ~500M+ Spanish speakers worldwide. This is especially relevant for schools and educational institutions in Latin America and Spain.

Implementation

• Follows the existing i18n architecture (TypeScript constants with useI18n hook)
• No new dependencies required
• All existing patterns preserved (same key structure as zh-CN and en-US)
• Voice/TTS/ASR already support Spanish through existing providers (OpenAI, Azure, Qwen, ElevenLabs)

Changes

• lib/i18n/types.ts — Added 'es-MX' to Locale type
• lib/i18n/*.ts — Added *EsMX translation constants (5 files)
• lib/i18n/index.ts — Registered es-MX translations
• lib/hooks/use-i18n.tsx — Updated detection and validation
• components/header.tsx — Added ES option to language selector
• components/generation/generation-toolbar.tsx — 3-language cycle for content generation
• app/page.tsx — Updated form state and browser detection
• lib/types/generation.ts — Updated language union types
• lib/server/classroom-generation.ts — Updated normalizeLanguage()
• lib/generation/scene-generator.ts — Updated language parameter type
• app/api/generate/scene-content/route.ts — Updated language cast

🤖 AI-assisted (Claude Code)