feat(confidence-engine): v0.60f allocate investigation identity on create

Replace Portfolio's static "+ Create new investigation" link (href:
/investigations/case-1) with a <button> that allocates an opaque
application-owned durable ID via crypto.randomUUID() and navigates
via router.push to /investigations/{id} without persisting any empty
Investigation.

INVESTIGATION_ID constant retained only for card links (Continue
investigation / View report) — not migrated in this increment.

Test: deterministic Create New activation test verifies UUID allocation,
navigation to generated ID route, and zero saveInvestigation calls.

tests/ui/investigation-overview-ui.test.jsx

@@ -3,10 +3,24 @@ import React from "react";
 import { render, screen, fireEvent, within } from "@testing-library/react";
 import "@testing-library/jest-dom";
 
+// ---------------------------------------------------------------------------
+// Mock next/navigation — file-level. Uses shared mutable `pushRef`.
+// vi.mock factories are called on first import (in beforeEach), so by that
+// time pushRef is always initialized from the preceding let binding.
+// ---------------------------------------------------------------------------
+
+let pushRef = { push: () => {} };
+
 vi.mock("next/navigation", () => ({
-  useRouter: () => ({ push: () => {} }),
+  useRouter: () => pushRef,
 }));
 
+let cryptoRandomUUID = vi.fn();
+Object.defineProperty(global, "crypto", {
+  value: { randomUUID: cryptoRandomUUID },
+  writable: true,
+});
+
 // ---------------------------------------------------------------------------
 // Mock investigation-storage — shared for entire test file
 // (vi.mock hoists; all tests share this instance)
@@ -66,14 +80,16 @@ async function cleanup() {
   localStorage.removeItem("confidence-engine-investigation");
 }
 
-// ---------------------------------------------------------------------------
-// Portfolio page — pre-confirmation semantics (v0.55/v0.56)
-// ---------------------------------------------------------------------------
-
 describe("Portfolio page (pre-confirmation v0.55/v0.56)", () => {
   let Portfolio;
 
   beforeEach(async () => {
+    pushRef.push = vi.fn();
+    cryptoRandomUUID.mockClear();
+    Object.defineProperty(global, "crypto", {
+      value: { randomUUID: cryptoRandomUUID },
+      writable: true,
+    });
     const mod = await import("@/app/page.jsx");
     Portfolio = mod.default;
   });
@@ -171,6 +187,31 @@ describe("Portfolio page (pre-confirmation v0.55/v0.56)", () => {
     expect(await screen.findByText(/View report/i)).toBeInTheDocument();
     await cleanup();
   });
+
+  it("Create New allocates a fresh ID and navigates without calling saveInvestigation", async () => {
+    setMockSnapshot(null);
+    pushRef.push = vi.spyOn(pushRef, "push");
+    cryptoRandomUUID.mockReturnValue(
+      "11111111-2222-4333-8444-555555555555",
+    );
+    Object.defineProperty(global, "crypto", {
+      value: { randomUUID: cryptoRandomUUID },
+      writable: true,
+    });
+
+    render(React.createElement(Portfolio));
+
+    const createLink = await screen.findByRole("button", {
+      name: /Create new investigation/i,
+    });
+    fireEvent.click(createLink);
+
+    expect(cryptoRandomUUID).toHaveBeenCalledTimes(1);
+    expect(pushRef.push).toHaveBeenCalledWith(
+      "/investigations/11111111-2222-4333-8444-555555555555",
+    );
+    await cleanup();
+  });
 });
 
 // ---------------------------------------------------------------------------