Fix code synchronization issues: unify language constants, enhance health check service, and resolve type inconsistencies

[Copilot]

This PR addresses critical synchronization issues discovered during a comprehensive codebase analysis. The main problems were inconsistent language constant definitions across multiple files, incorrect health check uptime calculations, and TypeScript compilation errors due to type mismatches.

Key Issues Fixed

Language Constants Synchronization

The codebase had three different language constant definitions that were out of sync:

• LANGUAGES in /src/types/index.ts (19 languages)
• SUPPORTED_LANGUAGES in /src/services/language-manager.ts (19 different languages)
• LANGUAGES in /src/bot/leitner-bot.ts (20+ languages)

This inconsistency caused issues where:

• Persian (fa) was supported in the language manager but missing from the main types
• Some languages were defined but not consistently available across components
• TypeScript strict typing caused compilation errors when mixing these constants

Solution: Unified all language definitions into a single source of truth in /src/types/index.ts with 25 supported languages, and updated all imports to use this centralized constant.

Health Check Service Issues

The health check service was calculating "uptime" incorrectly as the execution time of the health check function rather than the actual service uptime:

// Before (incorrect)
const uptime = Date.now() - startTime; // Only measures function execution time

// After (correct)  
const uptime = Date.now() - serviceStartTime; // Measures actual service uptime

Solution: Implemented proper service uptime tracking using a global serviceStartTime variable and enhanced the service with persistent system stats storage in KV store.

Environment Compatibility

The admin API was using Node.js-specific process.version and process.platform properties that are not available in Cloudflare Workers:

// Before (incompatible)
nodeVersion: process.version || 'unknown',
platform: process.platform || 'unknown',

// After (compatible)
nodeVersion: 'cloudflare-worker',
platform: 'cloudflare-worker',

TypeScript Type Safety

Fixed multiple TypeScript compilation errors related to strict typing of language button arrays and callback structures. Added proper type annotations to ensure type safety while maintaining flexibility.

Impact

• ✅ Build Status: All TypeScript compilation errors resolved
• ✅ Language Support: Consistent 25-language support across all components
• ✅ Monitoring: Enhanced health check service with proper uptime and system stats
• ✅ Runtime Compatibility: Full Cloudflare Workers environment compatibility
• ✅ Type Safety: Improved type definitions and error handling

Testing

• All changes have been validated with successful TypeScript compilation
• Language fallback mechanism verified for unsupported interface languages
• Health check service tested for proper uptime calculation
• Import structure confirmed with no circular dependencies

The codebase is now fully synchronized with consistent language support, proper monitoring capabilities, and zero compilation errors.

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