refactor(cli/create): collapse install-and-migrate into single helper

Simplify follow-up: the standalone and monorepo branches in vp create
were each carrying the same 7-step block (setPackageManager → yarn
.yarnrc.yml → progress update → runViteInstall → migrate prompts),
differing only in the install cwd. The yarn caveat comment was
duplicated verbatim in both blocks.

Fold both blocks plus the previously separate `migrateLintFmtTools`
arrow into a single `installAndMigrate(installCwd)` closure. The WHY
comments live once above the helper. Net -26 lines in create/bin.ts
with no behavior change; all four package managers (pnpm/npm/yarn/bun)
still migrate `vite@9.0.5 --template react-ts` correctly end-to-end.

Author: fengmk2

packages/cli/src/create/bin.ts

@@ -899,23 +899,6 @@ Use \`vp create --list\` to list all available templates, or run \`vp create --h
   });
   resumeCreateProgress();
 
-  // Auto-migrate ESLint → Oxlint and Prettier → Oxfmt after install #1 so
-  // `@oxlint/migrate` can resolve imports from eslint.config.js, but before
-  // the vite-plus rewrite so the generated .oxlintrc/.oxfmtrc get merged
-  // into vite.config.ts — matching `vp migrate`. Always non-interactive;
-  // Vite+ is opinionated about oxlint/oxfmt. Gated on install success so
-  // VP_SKIP_INSTALL snap tests don't hit ERR_MODULE_NOT_FOUND.
-  const migrateLintFmtTools = async (installed: boolean) => {
-    if (!installed) {
-      return;
-    }
-    updateCreateProgress('Migrating lint and format tools');
-    pauseCreateProgress();
-    await promptEslintMigration(fullPath, /* interactive */ false);
-    await promptPrettierMigration(fullPath, /* interactive */ false);
-    resumeCreateProgress();
-  };
-
   // The migrate-before-rewrite reorder is only needed when the template
   // actually ships ESLint or Prettier (e.g. `create-vite --template
   // react-ts`). Builtin templates (vite:library, vite:application,
@@ -926,6 +909,36 @@ Use \`vp create --list\` to list all available templates, or run \`vp create --h
     detectEslintProject(fullPath).hasDependency || detectPrettierProject(fullPath).hasDependency;
 
   let installSummary: CommandRunSummary | undefined;
+
+  // For templates that ship ESLint/Prettier, install template deps first so
+  // `@oxlint/migrate` can resolve eslint.config.js's plugin imports, then
+  // migrate before the vite-plus rewrite so the generated .oxlintrc/.oxfmtrc
+  // get merged into vite.config.ts — matching `vp migrate`. Pin the
+  // packageManager field (vite_install hardcodes pnpm in CI/non-TTY when no
+  // signal is present) and force yarn's classic node_modules layout (PnP
+  // zip entries break @oxlint/migrate's fileURLToPath resolution).
+  const installAndMigrate = async (installCwd: string) => {
+    setPackageManager(fullPath, workspaceInfo.downloadPackageManager);
+    if (workspaceInfo.packageManager === PackageManager.yarn) {
+      const yarnrcPath = path.join(fullPath, '.yarnrc.yml');
+      if (!fs.existsSync(yarnrcPath)) {
+        fs.writeFileSync(yarnrcPath, 'nodeLinker: node-modules\n');
+      }
+    }
+    updateCreateProgress('Installing dependencies');
+    installSummary = await runViteInstall(installCwd, options.interactive, installArgs, {
+      silent: compactOutput,
+    });
+    if (installSummary.status !== 'installed') {
+      return;
+    }
+    updateCreateProgress('Migrating lint and format tools');
+    pauseCreateProgress();
+    await promptEslintMigration(fullPath, /* interactive */ false);
+    await promptPrettierMigration(fullPath, /* interactive */ false);
+    resumeCreateProgress();
+  };
+
   if (isMonorepo) {
     if (!compactOutput) {
       prompts.log.step('Monorepo integration...');
@@ -991,28 +1004,7 @@ Use \`vp create --list\` to list all available templates, or run \`vp create --h
 
     updateWorkspaceConfig(projectDir, workspaceInfo);
     if (shouldMigrateLintFmtTools) {
-      // Pin the packageManager field before install so `vp install` honors
-      // the user's `--package-manager` choice instead of falling back to
-      // pnpm (the hardcoded non-interactive/CI default in vite_install).
-      setPackageManager(fullPath, workspaceInfo.downloadPackageManager);
-      // Yarn Berry's default Plug'n'Play stores deps inside .yarn/cache/*.zip,
-      // which @oxlint/migrate can't resolve (ESM's fileURLToPath over a zip
-      // entry throws MODULE_NOT_FOUND). Force classic node_modules layout so
-      // the migration step can import the template's ESLint plugins.
-      if (workspaceInfo.packageManager === PackageManager.yarn) {
-        const yarnrcPath = path.join(fullPath, '.yarnrc.yml');
-        if (!fs.existsSync(yarnrcPath)) {
-          fs.writeFileSync(yarnrcPath, 'nodeLinker: node-modules\n');
-        }
-      }
-      updateCreateProgress('Installing dependencies');
-      installSummary = await runViteInstall(
-        workspaceInfo.rootDir,
-        options.interactive,
-        installArgs,
-        { silent: compactOutput },
-      );
-      await migrateLintFmtTools(installSummary.status === 'installed');
+      await installAndMigrate(workspaceInfo.rootDir);
     }
     updateCreateProgress('Integrating into monorepo');
     rewriteMonorepoProject(fullPath, workspaceInfo.packageManager, undefined, compactOutput);
@@ -1031,25 +1023,7 @@ Use \`vp create --list\` to list all available templates, or run \`vp create --h
     });
   } else {
     if (shouldMigrateLintFmtTools) {
-      // Pin the packageManager field before install so `vp install` honors
-      // the user's `--package-manager` choice instead of falling back to
-      // pnpm (the hardcoded non-interactive/CI default in vite_install).
-      setPackageManager(fullPath, workspaceInfo.downloadPackageManager);
-      // Yarn Berry's default Plug'n'Play stores deps inside .yarn/cache/*.zip,
-      // which @oxlint/migrate can't resolve (ESM's fileURLToPath over a zip
-      // entry throws MODULE_NOT_FOUND). Force classic node_modules layout so
-      // the migration step can import the template's ESLint plugins.
-      if (workspaceInfo.packageManager === PackageManager.yarn) {
-        const yarnrcPath = path.join(fullPath, '.yarnrc.yml');
-        if (!fs.existsSync(yarnrcPath)) {
-          fs.writeFileSync(yarnrcPath, 'nodeLinker: node-modules\n');
-        }
-      }
-      updateCreateProgress('Installing dependencies');
-      installSummary = await runViteInstall(fullPath, options.interactive, installArgs, {
-        silent: compactOutput,
-      });
-      await migrateLintFmtTools(installSummary.status === 'installed');
+      await installAndMigrate(fullPath);
     }
     updateCreateProgress('Applying Vite+ project setup');
     rewriteStandaloneProject(fullPath, workspaceInfo, undefined, compactOutput);