Refactor main.go into CLI package and extend audit test coverage

- Move all CLI logic from main.go into new cli package for better modularity
- main.go is now extremely slim (18 lines), only importing and calling cli package
- Add comprehensive audit package test coverage:
  - Edge cases (empty fields, special characters, long URLs, custom reasons)
  - Different log levels and filtering behavior
  - Nil logger/request handling with graceful panic testing
  - Enhanced HTTPRequestToAuditRequest tests for all HTTP methods
  - Interface compliance, JSON/text handlers, and discard handler testing
  - 11 test functions with 24 sub-tests providing thorough coverage

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: f0ssel