Stabilize collection cleanup E2E and preserve release artifacts

[Copilot]

The collections E2E suite was flaking because cleanup tried to click a visible Leave button before it became interactable. The rolling release workflow was also deleting downloaded artifacts by checking out the repo after populating dist/, which broke version stamping.

• E2E cleanup timing

  • Update removeAllCollections() to wait for the first Leave button to become enabled before clicking.
  • Give the click a bounded explicit timeout so cleanup tolerates slower UI state transitions.

• Release artifact preservation

  • Reorder the rolling release job so actions/checkout runs before actions/download-artifact.
  • Keep dist/ intact for the subsequent slopterm-version.txt stamp and release asset upload.

const leave = page.getByRole('button', { name: 'Leave' }).first()
if (!(await leave.isVisible().catch(() => false))) return
await expect(leave).toBeEnabled({ timeout: 15_000 })
await leave.click({ timeout: 15_000 })