🎨 Palette: Improve contributor UX and consistency in CONTRIBUTING.md

[google-labs-jules]

This PR introduces several micro-UX and developer experience (DX) improvements to the CONTRIBUTING.md file to make it more intuitive and accessible for potential contributors.

Key changes:

• 💡 Help Wanted Link: Converted the plain-text reference to the 'help wanted' label into a direct, pre-filtered link to the GitHub issues page. This reduces friction for new contributors looking for tasks.
• 🎯 Tooling Alignment: Updated the setup instructions to use mise run install instead of mise install to ensure project-specific task logic is correctly executed.
• ♿ Accessibility & Polish: Corrected spelling inconsistencies ("licence" to "license") and punctuation typos (".. etc" to "etc.") to maintain professional documentation standards.

Verification:

• ✅ Documentation build verified with uv run mkdocs build.
• ✅ All repository tests passed with uv run pytest.
• ✅ No regressions in template functionality.

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PR created automatically by Jules for task 14041523791916114696 started by @amrabed

[google-labs-jules]

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