feat: add --verbose flag shortcut for log level

[ahfoysal]

Implemented OWASP/DockSec #129.

What changed

• Added CLI option to set when not already set.
• Ensured verbose mapping runs before output initialization.
• Kept command output tests explicit and non-breaking:
  • sets env var when unset
  • does not overwrite pre-set
• Updated README usage examples with verbose command example.

Validation

• ============================= test session starts ==============================
  platform darwin -- Python 3.9.6, pytest-8.4.2, pluggy-1.6.0
  rootdir: /Users/apple/Documents/DockSec
  configfile: pyproject.toml
  plugins: anyio-4.12.1, langsmith-0.4.37
  collected 53 items

tests/test_cli.py ..................................................... [100%]

============================== 53 passed in 2.05s ============================== (53 passed)