refactor(tests): centralize test harness boilerplate into bundle.mjs helper

tests/run-migration-test.mjs

@@ -8,37 +8,22 @@
 //   - idempotency (original .md untouched)
 // Builds src/main/migration.ts with esbuild (no Electron needed).
 // Run with: node tests/run-migration-test.mjs
-import esbuild from "esbuild";
 import fs from "fs";
 import os from "os";
 import path from "path";
-import url from "url";
+import { bundleForTest } from "./helpers/bundle.mjs";
 
-const out = path.join(os.tmpdir(), `folio-migration-${process.pid}.mjs`);
-const entry = path.resolve(".folio-mig-test-entry.ts");
-fs.writeFileSync(
-  entry,
-  `
+const { mod, cleanupBundle } = await bundleForTest({
+  name: "folio-migration",
+  entrySource: `
 export { migrateChapterToNative, migrateBookToNative, isNativeChapter } from "./src/main/migration.ts";
 export { createBook, loadBook, saveMeta } from "./src/main/project.ts";
 export { setChapterContent, getChapterContent } from "./src/main/chapters.ts";
 export { markdownToNative } from "./src/main/markdown-to-native.ts";
 export { parseChapter, serializeChapter, migrateDoc, getChapterDoc, nativeChapterFile, CURRENT_DOC_SCHEMA_VERSION, isValidDoc } from "./src/main/native-doc.ts";
 export { getRecoveryRoot, _resetSessionBackupGuard } from "./src/main/backup.ts";
-`
-);
-await esbuild.build({
-  entryPoints: [entry],
-  bundle: true,
-  platform: "node",
-  format: "esm",
-  outfile: out,
-  write: true,
-  logLevel: "silent",
+`,
 });
-fs.rmSync(entry, { force: true });
-
-const mod = await import(url.pathToFileURL(out).href);
 const {
   createBook,
   setChapterContent,
@@ -291,7 +276,7 @@ ok(
 // ---------------------------------------------------------------------------
 // Cleanup
 // ---------------------------------------------------------------------------
-fs.rmSync(out, { force: true });
+cleanupBundle();
 fs.rmSync(book, { recursive: true, force: true });
 for (const d of backups) {
   fs.rmSync(path.join(getRecoveryRoot(), d), { recursive: true, force: true });