fix(aitools): support Copilot project scope

[50sotero]

Summary

Enables project-scoped Databricks AI skills installs for GitHub Copilot by mapping Copilot project skills to .github/skills.

Changes

• Mark the Copilot agent as project-scope compatible
• Configure Copilot project installs under .github/skills
• Add regression coverage for Copilot project-scope support and path resolution

Test Plan

• go test ./libs/aitools/... ./cmd/aitools
• LSP diagnostics clean on modified Go files

Fixes databricks/databricks-agent-skills#98

[github-actions]

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Trigger:
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Inputs:

• PR number: 5675
• Commit SHA: 3245d6814bacf5d51b09f3fe890b535c7b39b143

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