feat: Add comprehensive improvements - CLI, error handling, and docs

- Add CLI argument parsing with clap (dry-run, max-concurrent options)
- Replace .env configuration with interactive prompts and TOML config
- Add BaseDirs-based configuration storage in ~/.config/noentropy/
- Improve Gemini API client with configurable model and timeout
- Add concurrent processing with semaphore for rate limiting
- Improve error handling with retry logic and exponential backoff
- Add comprehensive README with installation and usage instructions
- Add config.example.toml template for users
- Update main.rs with better UX and colored output
- Add lib.rs exports for config module
- Refactor error response parsing for cleaner code
- Update API endpoint to use configurable model parameter
- Add proper error type handling in gemini_errors.rs

src/lib.rs

@@ -1,4 +1,5 @@
 pub mod cache;
+pub mod config;
 pub mod files;
 pub mod gemini;
 pub mod gemini_errors;