[WIP] Add deploy GitHub action for tag pushes

[Copilot]

• Create .github/workflows/deploy.yml that triggers on tag push (v*), builds the extension, and publishes to the VS Code Marketplace using @vscode/vsce publish with VSCE_PAT passed securely as an environment variable

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[rbnswartz]

@copilot try again

[Copilot]

@copilot try again

Redone in d36e562. Changes from the previous version:

• Switched from deprecated vsce to @vscode/vsce (the current official package)
• Pass VSCE_PAT securely via env: instead of exposing it as a -p CLI argument (which could appear in logs)
• Removed the redundant explicit compile step since npm run package already invokes vscode:prepublish which runs the production build