[Repo] Port editors/vscode/src/extension.ts to .affine once #35 lands

[hyperpolymath]

Problem

editors/vscode/src/extension.ts is the only TypeScript file under editors/. It exists because AffineScript currently has no Node-target backend, and VS Code extensions have to ship a Node-callable entry point pinned by package.json's main field.

It's documented as an approved exemption in .claude/CLAUDE.md (see TypeScript Exemptions table). The unblock condition is #35.

Acceptance criteria

• Add Node-target backend + vscode-API bindings to enable .affine VS Code extensions #35 has landed (Node-target codegen produces a JS file consumable as a CommonJS module).
• Port the extension to editors/vscode/src/extension.affine.
• Update editors/vscode/package.json main to point at the AffineScript-compiled artefact.
• Verify activation, command registration, LSP client wiring, and disposable cleanup all work end-to-end.
• Remove the editors/vscode/src/extension.ts row from the TypeScript Exemptions table in .claude/CLAUDE.md.

Origin

TS-elimination audit, 2026-05-02 (recommendation #7). Local audit at ~/dev/affinescript/.claude/CLAUDE.md notes the exemption.

Dependencies

• Add Node-target backend + vscode-API bindings to enable .affine VS Code extensions #35 (Node-target backend + vscode-API bindings)