test: add E2E tests for threads, auth, and error handling

Also fix CandidateListItem to not use Reorder.Item when isActive=false,
which caused a framer-motion crash on resolved thread detail pages.

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

e2e/error-handling.spec.ts

@@ -0,0 +1,59 @@
+import { expect, test } from "@playwright/test";
+
+test.describe("Error handling — non-existent routes", () => {
+	test("non-existent thread does not white-screen", async ({ page }) => {
+		await page.goto("/threads/99999");
+
+		// React Query retries failed requests (default 3 times with backoff) before
+		// setting isError=true. Wait for the page to leave loading state and show content.
+		// The thread detail page renders "Thread not found" + "Back to planning" link on error.
+		await expect(page.getByText("Back to planning")).toBeVisible({
+			timeout: 30000,
+		});
+		await expect(page.getByText("Thread not found")).toBeVisible({
+			timeout: 5000,
+		});
+	});
+
+	test("non-existent setup does not white-screen", async ({ page }) => {
+		await page.goto("/setups/99999");
+		await page.waitForLoadState("networkidle");
+
+		// Setup detail shows "Setup not found." when data is null (no retry — isLoading=false, data=undefined)
+		// The setup query resolves with undefined rather than throwing for missing items.
+		// Check that the page has content (not a blank screen).
+		const body = page.locator("body");
+		await expect(body).not.toBeEmpty();
+
+		// Navigation header should be visible (app did not crash)
+		await expect(page.getByText("GearBox")).toBeVisible({ timeout: 5000 });
+
+		// Wait for setup data to load; it will show "Setup not found." when done
+		await expect(page.getByText("Setup not found.")).toBeVisible({
+			timeout: 30000,
+		});
+	});
+
+	test("app recovers after bad route — dashboard loads fine", async ({
+		page,
+	}) => {
+		// Navigate to a non-existent thread first
+		await page.goto("/threads/99999");
+
+		// The page should render without crashing — wait for the error state
+		// (React Query retries before showing isError state, so use a long timeout)
+		await expect(page.getByText("Back to planning")).toBeVisible({
+			timeout: 30000,
+		});
+
+		// Now navigate to the dashboard
+		await page.goto("/");
+		await page.waitForLoadState("networkidle");
+
+		// Dashboard should load normally
+		await expect(page.getByText("GearBox")).toBeVisible({ timeout: 5000 });
+		await expect(page.getByRole("heading", { name: "Collection" })).toBeVisible(
+			{ timeout: 5000 },
+		);
+	});
+});