Fix Ruff format drift causing CI Lint (ruff) failure

[Copilot]

The Lint (ruff) GitHub Actions job was failing because ruff format --check detected formatting drift in a small set of files. This PR applies only formatter-aligned edits to the CI-flagged files so the lint job can pass without changing behavior.

• Scope: formatting-only updates in CI-flagged files

  • Updated formatting in:
    • src/cairn/cli.py
    • src/cairn/db/fragments.py
    • src/cairn/flight/types.py
    • src/cairn/storage/cas.py
    • src/cairn/storage/s3.py
    • tests/integration/test_migration_kill.py

• No semantic changes

  • Edits are limited to line wrapping and call formatting (e.g., multi-line vs single-line expressions), with no logic, control-flow, or API changes.

• Representative formatter change

  # before
  raise ValueError("a purity policy that authorizes reuse requires qualification_runs >= 2")
  
  # after
  raise ValueError(
      "a purity policy that authorizes reuse requires qualification_runs >= 2"
  )