Add self-contained e2e test harness with ephemeral PocketBase

Previously, 15 e2e tests were skipped because TEST_USER_EMAIL and
TEST_USER_PASSWORD env vars weren't set. Now the test harness:

- Starts a fresh PocketBase instance in /tmp on port 8091
- Creates admin user, collections, and API rules automatically
- Seeds test user with period data for authenticated tests
- Cleans up temp directory after tests complete

Also fixes:
- Override toggle tests now use checkbox role (not button)
- Adds proper wait for OVERRIDES section before testing toggles
- Suppresses document.cookie lint warning with explanation

Test results: 64 e2e tests pass, 1014 unit tests pass

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

e2e/calendar.spec.ts

@@ -47,8 +47,11 @@ test.describe("calendar", () => {
     });
 
     test("displays calendar page with heading", async ({ page }) => {
-      // Check for calendar heading
-      const heading = page.getByRole("heading", { name: /calendar/i });
+      // Check for the main calendar heading (h1)
+      const heading = page.getByRole("heading", {
+        name: "Calendar",
+        exact: true,
+      });
       await expect(heading).toBeVisible();
     });