fix: enforce GitHub author commit threshold

[thejonali]

Summary

Enforces the existing GitHub project selection rule that selected repositories must have at least 4 author commits.

Previously, the prompt required author_commit_count >= 4, but the code only filtered out repositories with exactly 0 author commits. As a result, repositories with 1-3 author commits could still be passed to the LLM and returned in the final selected GitHub projects.

Changes

• Filters candidate GitHub projects before LLM selection when author_commit_count < 4.
• Filters LLM-selected projects again before returning them, so invalid selections cannot pass through even if the model returns them.

Validation

• Ran the resume workflow against a GitHub account
• Ran python -m py_compile github.py
• Confirmed repos < 4 were not included

Closes #269