test: add e2e coverage for faculty assignments and grading

[ishad05]

What this tests

• API level (faculty-assignments.spec.ts, 7 tests)
  • Creating an assignment as a draft, publishing it now, and scheduling it for later
  • Rejecting a scheduled assignment when no publish date is given
  • Correct naming series for graded vs not graded assignments
  • Listing a cohort's assignments with the right submission counts
  • Grading a submission and publishing the grade now, or saving it as a draft

UI level (faculty-assignments-ui.spec.ts, 2 tests)

• A faculty member creates and publishes an assignment from the create sheet and sees it in the list
• A faculty member grades a submission from the detail page and sees the grade published

How it is set up

• New faculty.setup.ts logs in a seeded faculty user and saves its session, same pattern as the existing student setup
• New helpers: createTestFaculty, createTestSubmission, cleanupTestGrades
• playwright.config.ts gains faculty-setup and chromium-faculty projects so the UI spec runs in a real faculty browser session
• The test faculty user gets CS17 Faculty plus System Manager, matching how real faculty accounts are provisioned