Add .prettierrc.json and refactor test files for improved formatting consistency:

- Introduced `.prettierrc.json` to enforce consistent code formatting across the project.
- Updated unit and e2e test files to address formatting issues, improve readability, and ensure alignment with the new Prettier configuration.

tests/e2e/superuser-system-status.smoke.spec.js

@@ -186,7 +186,8 @@ const longReasonSnapshot = {
       configured: true,
       probe_supported: true,
       status: "configured",
-      status_reason: "Shelly cloud credentials are configured, but no known device id is available for a safe read-only probe.",
+      status_reason:
+        "Shelly cloud credentials are configured, but no known device id is available for a safe read-only probe.",
       status_reason_key: "shelly_no_device_id",
       status_reason_params: {},
       checked_at: "2026-04-08T08:45:00.000Z",
@@ -231,7 +232,9 @@ test.describe("Superuser system status smoke", () => {
     await primeSuperuserSession(page);
   });
 
-  test("@smoke superuser status dashboard renders Danish translations for degraded infrastructure and recent sessions", async ({ page }) => {
+  test("@smoke superuser status dashboard renders Danish translations for degraded infrastructure and recent sessions", async ({
+    page,
+  }) => {
     await installSystemStatusMock(page, degradedSnapshot);
 
     await page.goto("/superuser");
@@ -286,10 +289,7 @@ test.describe("Superuser system status smoke", () => {
     expect(pillBox).not.toBeNull();
     expect(reasonBox).not.toBeNull();
 
-    const headerBottom = Math.max(
-      titleBox.y + titleBox.height,
-      pillBox.y + pillBox.height
-    );
+    const headerBottom = Math.max(titleBox.y + titleBox.height, pillBox.y + pillBox.height);
 
     expect(reasonBox.y).toBeGreaterThanOrEqual(headerBottom - 1);
   });