tests(e2e): Refactor various tests

Goals:

- speedup
- less flakiness
- best practices and more use
- documentation

config:
- sync ports in Makefile and playwright config
  (otherwise, some tests fail locally because they assert the full URL including the (wrong) port)
- even more generous timeouts
- limit workers to one again (because I finally understand how
  Playwright works)
- allow nested functions to group them together with the related test

all:

- deprecate waitForLoadState('networkidle')
  - it is discouraged as per https://playwright.dev/docs/api/class-page#page-wait-for-load-state
  - I could not find a usage that seems to require it actually (see
    added documentation in README)
  - adding an exception should be made explicitly
  - it does not do what you might expect anyway in most cases
- only log in when necessary

webauthn:

- verify that login is possible after disabling key
- otherwise, the cleanup was not necessary after the previous refactor to create a fresh user each

issue-sidebar / WIP toggle:

- split into smaller chunks
- restore original state first
- add missed assertion to fix race condition (not waiting
  before state was reached)
- explicitly toggle the state to detect mismatch earlier

issue-sidebar / labels:

- restore original state first
- better waiting for background request

tests/e2e/dashboard-ci-status.test.e2e.ts

@@ -15,10 +15,9 @@ test('Correct link and tooltip', async ({browser}, workerInfo) => {
   const response = await page.goto('/?repo-search-query=test_workflows');
   expect(response?.status()).toBe(200);
 
-  await page.waitForLoadState('networkidle');
-
   const repoStatus = page.locator('.dashboard-repos .repo-owner-name-list > li:nth-child(1) > a:nth-child(2)');
-
+  // wait for network activity to cease (so status was loaded in frontend)
+  await page.waitForLoadState('networkidle'); // eslint-disable-line playwright/no-networkidle
   await expect(repoStatus).toHaveAttribute('href', '/user2/test_workflows/actions', {timeout: 10000});
   await expect(repoStatus).toHaveAttribute('data-tooltip-content', 'Failure');
 });