docs: add API key permissions/scopes documentation (#1841)

[saifyxpro]

Summary

Adds comprehensive documentation for required permissions/scopes of all API keys used in bolt.diy to improve security and help users configure minimal required access.

Changes

• ✅ New docs/api-keys.md file - Comprehensive API key permissions documentation
• ✅ Updated README.md - Added reference link to new documentation
• 📋 Documented 19+ AI providers with minimal required permissions
• 🔐 Security best practices included for key management
• 🛠️ Troubleshooting guide for common permission issues
• 🌐 Cloud service integrations (GitHub, GitLab, Vercel, Netlify, Supabase)

Features Added

• Detailed permission requirements for each API provider
• Security best practices and key rotation guidelines
• Environment variable setup instructions
• Troubleshooting section for common issues
• Links to provider documentation for obtaining keys

Related Issue

Fixes #1841

Testing

• ✅ All API key environment variables documented
• ✅ Documentation organized with clear table of contents
• ✅ Security considerations properly addressed
• ✅ Integration with existing README.md