✨ feat: support reading commit message from a file

[welpo]

Summary

Add support for reading commit messages from a file via a new --file flag. This allows direct input of commit messages from files as an alternative to command-line arguments or stdin.

Related issue

#179

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How has this been tested?

• Manual tests
• Unit tests
• Integration tests

Added comprehensive test suite in tests/lint/test_file_input.rs covering:

• Reading valid files
• Handling empty files
• Processing files with comments
• Handling multiline messages
• Error cases

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Type of change

• Bug fix (fixes an issue without altering functionality)
• New feature (adds non-breaking functionality)
• Breaking change (alters existing functionality)
• UI/UX improvement (enhances user interface without altering functionality)
• Refactor (improves code quality without altering functionality)
• Documentation update
• Other (please describe below)

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Checklist

• I have read the contributing guidelines.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My code follows the code style of this project.
• I have formatted the code with cargo fmt.
• My change requires updating the documentation.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.25%. Comparing base (2550ee5) to head (9376c9c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #198   +/-   ##
=======================================
  Coverage   98.24%   98.25%           
=======================================
  Files          12       12           
  Lines        1310     1317    +7     
=======================================
+ Hits         1287     1294    +7     
  Misses         23       23           

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