test(vscode): in-editor smoke harness via @vscode/test-electron (Closes #139)

[hyperpolymath]

Summary

• Adds editors/vscode/test/ — a headless extension-host runner that loads the compiled out/extension.cjs in a real VS Code via @vscode/test-electron and asserts the four acceptance bullets from [QA] In-editor end-to-end smoke test for the .affine VS Code extension #139.
• Wires a vscode-smoke job into .github/workflows/ci.yml (Node 20 + xvfb-run + npm test). The compiled extension.cjs is already checked in (Add Node-target backend + vscode-API bindings to enable .affine VS Code extensions #35 Phase 3) so the smoke job does not need the OCaml toolchain — only the Node-side test deps.
• Records the Node-only runner as the second Runtime Exemption in .claude/CLAUDE.md, paralleling the existing affine-vscode-publish.yml carve-out (Publish @hyperpolymath/affine-vscode to npm (eliminate vendoring) #104). Scope is strictly editors/vscode/test/; no production code adopts Node.

Acceptance-criteria mapping (from #139)

#	AC bullet	Test
1	Extension activates without error	AC1 — extensions.getExtension(...).activate() resolves; isActive is true
2	All five affinescript.{check,eval,compile,format,restartLsp} register and run	AC2a — all five appear in getCommands(true). AC2b — executeCommand on each resolves without throwing
3	LSP client starts, attaches, and restartLsp cycles it cleanly	AC3 — two back-to-back restartLsp invocations both resolve. (Full attach path activates only when affinescript-lsp is on PATH; CI exercises the documented showWarningMessage short-circuit. Set AFFINESCRIPT_LSP_PATH to a real binary to drive the attach branch.)
4	Disposables cleaned up on deactivate	AC4 — calls the extension's exported deactivate() and asserts it resolves without throwing

Files

• editors/vscode/test/runTest.js — driver: downloads VS Code, launches with --extensionDevelopmentPath + --extensionTestsPath.
• editors/vscode/test/suite/index.js — Mocha entry the host invokes; discovers *.test.js.
• editors/vscode/test/suite/extension.test.js — the four acceptance tests above.
• editors/vscode/package.json — adds @vscode/test-electron, mocha, glob to devDependencies; adds npm test script.
• .github/workflows/ci.yml — new vscode-smoke job.
• .claude/CLAUDE.md — second Runtime Exemption row.

Test plan

• Local: from editors/vscode/, fetch deps and run xvfb-run npm test (or npm test on a desktop session) — all four acceptance tests pass against the checked-in out/extension.cjs.
• CI: the new vscode-smoke job goes green on this PR.
• Manual cross-check: install the packaged .vsix in VS Code, open a .affine file, run each of the five commands — observed behaviour matches what the harness asserts.

Closes #139.

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