docs(12-02): create comprehensive configuration guide

- Document all required environment variables (GITHUB_TOKEN, OWNER, REPO)
- Document optional AI provider configuration (Anthropic, OpenAI, Google, Perplexity)
- Document AI model and task generation configuration options
- Add MCP client configuration examples (Claude, Cursor, VS Code, Windsurf, Roocode)
- Add Docker configuration with docker-compose example
- Include security best practices for tokens and API keys
- Add configuration validation reference

Author: kunwarVivek