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/period-logging.spec.ts

@@ -73,18 +73,20 @@ test.describe("period logging", () => {
     test("period history shows table or empty state", async ({ page }) => {
       await page.goto("/period-history");
 
+      // Wait for loading to complete
+      await page.waitForLoadState("networkidle");
+
       // Look for either table or empty state message
       const table = page.getByRole("table");
-      const emptyState = page.getByText(/no period|no data|start tracking/i);
+      const emptyState = page.getByText("No period history found");
+      const totalText = page.getByText(/\d+ periods/);
 
       const hasTable = await table.isVisible().catch(() => false);
-      const hasEmpty = await emptyState
-        .first()
-        .isVisible()
-        .catch(() => false);
+      const hasEmpty = await emptyState.isVisible().catch(() => false);
+      const hasTotal = await totalText.isVisible().catch(() => false);
 
-      // Either should be present
-      expect(hasTable || hasEmpty).toBe(true);
+      // Either table, empty state, or total count should be present
+      expect(hasTable || hasEmpty || hasTotal).toBe(true);
     });
 
     test("period history shows average cycle length if data exists", async ({