🔧 Fix Environment Validation Import Error

✅ Build Issue Resolved:
- Fixed missing validateEnvironmentVariables function import in startup-validation.ts
- Updated to use correct functions: validateAIProviderEnv and validateFirebaseEnv
- Maintained all validation functionality while fixing the import error

🛠️ Changes Made:
- src/lib/startup-validation.ts: Fixed import and function usage
- Updated validation logic to use existing functions from env-validation.ts
- Preserved all error handling and warning messages

🎯 Root Cause:
- startup-validation.ts was importing non-existent validateEnvironmentVariables function
- This caused TypeError during build process for pages using startup validation

✅ Expected Result:
- Successful Netlify builds without function import errors
- Proper environment validation during startup
- All pages build successfully including /blog
- AI-first SEO features preserved

🚀 Status: Ready for Production Deployment

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