F2 SLICE-5: @vscode/test-electron host E2E (create→reload→re-anchor→orphan) (#4)

Drives the extension's returned ThreadController API + asserts the on-disk
sidecar and rendered Comments state (spec §6.8 fallback). All 4 host tests
green against VS Code 1.124.0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/e2e/suite/index.ts

@@ -0,0 +1,13 @@
+import * as path from "path";
+import Mocha from "mocha";
+import { glob } from "glob";
+
+export async function run(): Promise<void> {
+  const mocha = new Mocha({ ui: "tdd", color: true, timeout: 60000 });
+  const testsRoot = path.resolve(__dirname);
+  const files = await glob("**/*.test.js", { cwd: testsRoot });
+  for (const f of files) mocha.addFile(path.resolve(testsRoot, f));
+  await new Promise<void>((resolve, reject) => {
+    mocha.run((failures) => (failures > 0 ? reject(new Error(`${failures} E2E test(s) failed`)) : resolve()));
+  });
+}