fix: Update link to CONTRIBUTING.md in PR template

[echarrod]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run node update-readme.js and verified that README.md is up to date.

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Description

• Generated link in PRs is broken (example: fix: Update playwright after tool name changes #348, and this MR)
• We could link to ../blobs/main/CONTRIBUTING.md, but then I think that isn't evaluated correctly in all views

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Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• Other (please specify):
  • Link fix

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Additional Notes

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull Request Overview

This PR fixes a broken relative link in the pull request template by replacing it with an absolute URL to the CONTRIBUTING.md file.

Key Changes:

• Updated the CONTRIBUTING.md link in the PR template from a relative path to an absolute GitHub URL to ensure it works correctly in all views.