Prepare repository for GitHub Marketplace publication

[SoulSniper-V2]

This PR prepares the repository for publication to the GitHub Marketplace.

Changes include:

1. Dependencies: Enabled pyyaml in requirements.txt to support YAML configuration files, which are used in the documentation and examples.
2. Core Logic:
   • Updated llm_validator/core.py to support loading YAML configuration files.
   • Fixed a bug where AssertionType was redefined in core.py, causing type mismatch errors when checking assertions (fixing "No handler for assertion type" warnings).
3. GitHub Action: Updated entrypoint.py to support YAML configuration files.
4. Documentation: Updated README.md to include a "GitHub Marketplace Usage" section, documenting inputs/outputs and providing a usage example.
5. Examples: Created missing example configuration files validators/code_review.yaml and validators/sales_plan.yaml referenced in the README.
6. Tests: Fixed incorrect test data in tests/test_core.py and verified all tests pass.
7. Maintenance: Added .gitignore to prevent committing build artifacts.

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PR created automatically by Jules for task 12980928740320497097 started by @SoulSniper-V2

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