Improve/code quality

[gchamon]

• fix issues presented by sonarcloud (reduce cognitive complexity by extracting helpers in curator.py,
  dav_app.py, subtitles.py, state.py, ui_live.py, dav_protocol.py; extract duplicated string literals
  into named constants in models.py/dav_app.py; use resp.read() instead of pass on urlopen; switch
  assertTrue(a > b) to assertGreater; drop _strip_secrets nested complexity into _strip_provider_token /
  _strip_opensubtitles_secrets)
• reimplement marquee-on-hover (plus add a work-item note under work-items/ and test coverage
  asserting the BuzzOverflowMarquee hook renders on archive/cache pages)
• consolidate Dockerfile RUN layers (merge the bootstrap mkdir/touch into the uv pip install layer)
• minor typing cleanups (e.g. Any import in dav_app.py, explicit set[str] annotations in curator.py)

[sonarqubecloud]

Quality Gate failed

Failed conditions
59.7% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud