feat(generators): ui byte-identical snapshot + dispatch entry + e2e test

- Adds ui.snapshot.json (28 entries) computed from packages/core-ui
- Wires CORE_PACKAGE_GENERATORS["ui"]: guard + emitTemplateTree +
  addToTranspilePackages + printUiNextSteps (web-tanstack/storybook
  wiring is printed, not generated — resists templating)
- Adds "ui" to the core-package generator choices list
- Adds core-package-ui.e2e.test.ts (byte-identical reconstruction)
  — passes in 14.6 s

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

turbo/generators/__tests__/core-package-ui.e2e.test.ts

@@ -0,0 +1,52 @@
+import { describe, it, expect } from "vitest";
+import { mkdtempSync, cpSync, readFileSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { execSync } from "node:child_process";
+import { join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { computeSnapshot } from "../lib/snapshot";
+import expectedSnapshot from "../__snapshots__/core-package/ui.snapshot.json";
+
+// Repo root is 2 levels up from turbo/generators/__tests__
+const REPO_ROOT = resolve(fileURLToPath(import.meta.url), "..", "..", "..", "..");
+
+/**
+ * Strip "@repo/core-ui" from a package.json file in the tmp tree.
+ * Required when simulating a fresh scaffold: core-ui does not exist yet
+ * but the snapshot was captured before removal. Apps in the current tree
+ * still list it as a dependency.
+ */
+function stripCoreUiDep(pkgJsonPath: string): void {
+  const raw = readFileSync(pkgJsonPath, "utf8");
+  const parsed = JSON.parse(raw) as Record<string, Record<string, string>>;
+  for (const section of ["dependencies", "devDependencies", "peerDependencies"] as const) {
+    if (parsed[section]?.["@repo/core-ui"]) {
+      delete parsed[section]["@repo/core-ui"];
+    }
+  }
+  writeFileSync(pkgJsonPath, JSON.stringify(parsed, null, 2) + "\n");
+}
+
+describe("e2e: core-package ui", () => {
+  it("byte-identical reconstruction matches snapshot", { timeout: 120_000 }, () => {
+    const tmp = mkdtempSync(join(tmpdir(), "e2e-ui-"));
+    cpSync(REPO_ROOT, tmp, {
+      recursive: true,
+      filter: (src) =>
+        !src.includes("node_modules") &&
+        !src.includes(".turbo") &&
+        !src.includes("packages/core-ui"),
+    });
+
+    // Strip @repo/core-ui from app package.json files so pnpm install
+    // succeeds without the package being present (simulating the post-removal state).
+    stripCoreUiDep(join(tmp, "apps", "web-next", "package.json"));
+    stripCoreUiDep(join(tmp, "apps", "web-tanstack", "package.json"));
+    stripCoreUiDep(join(tmp, "apps", "storybook", "package.json"));
+
+    execSync(`cd ${tmp} && pnpm install --frozen-lockfile=false`, { stdio: "ignore" });
+    execSync(`cd ${tmp} && pnpm turbo gen core-package --args ui`, { stdio: "ignore" });
+    const result = computeSnapshot(join(tmp, "packages/core-ui"));
+    expect(result).toEqual(expectedSnapshot);
+  });
+});