📝 docs(env): update environment variable documentation
- add .env.example file with comprehensive environment variable template
- update ui-architecture.md to reflect actual environment variable configuration
- include server configuration, database, Redis, MinIO, OSS and JWT settings
- add instructions to copy .env.example to .env for local configuration
🔧 chore(env): add environment variable template file
- create .env.example with all necessary configuration variables
- set default values for common settings like ports and URLs
- mark sensitive fields with placeholder text (your_password_here, etc.)
- include comments explaining each configuration section