Add VS Code extension release workflow

[sdairs]

Summary

• Adds release-vscode.yml GitHub Actions workflow that builds platform-specific .vsix packages with the clickhouse-lsp binary bundled inside (rust-analyzer pattern)
• Builds for 6 platforms: linux-x64, linux-arm64, darwin-x64, darwin-arm64, win32-x64, win32-arm64
• Updates the extension to prefer the bundled server binary before falling back to $PATH
• Publishes to VS Code Marketplace, Open VSX, and GitHub Releases on version tags (v*)
• Can also be triggered manually via workflow_dispatch
• All releases are marked as pre-release (--pre-release flag) so they show an experimental badge on the Marketplace. Remove the flag from the workflow when ready for stable releases.
• Adds a marketplace README (packages/vscode/README.md) with a prominent experimental warning

How it works

1. Build job (matrix): Compiles clickhouse-lsp for each target, copies it into packages/vscode/server/, builds the TypeScript extension, packages a platform-specific .vsix via vsce package --pre-release --target
2. Publish job: Downloads all .vsix artifacts and publishes to VS Code Marketplace (requires VSCE_PAT secret) and optionally Open VSX (OVSX_PAT secret)
3. Release job: Creates a GitHub Release with all .vsix files attached

Setup required

• Add VSCE_PAT secret (VS Code Marketplace personal access token)
• Optionally add OVSX_PAT secret for Open VSX publishing
• To release: push a tag like git tag v0.1.0 && git push --tags

Test plan

• Trigger workflow manually via workflow_dispatch (without publish) to verify builds succeed
• Verify .vsix artifacts are produced for all 6 platforms
• Install a built .vsix locally and confirm the bundled LSP server starts
• Verify serverPath setting still overrides the bundled binary
• Confirm pre-release badge appears on the Marketplace listing

🤖 Generated with Claude Code