Rewrite CI to lint/typecheck/audit/test only; add HPC deployment path

- Replace the Docker build/publish CI stages with ruff (lint + format
  check), ty (type check), pip-audit, and pytest run directly against
  python:3.11-slim; Docker remains for manual/server deployment only.
- Swap black/pylint/mypy for ruff/ty across pyproject.toml, and fix
  every resulting lint, format, and type diagnostic in gallery/ and
  plotstyle/.
- Fix tests broken/stale from before the package restructuring: wrong
  `utils.*` import paths, mock patch targets pointed at the wrong
  module, and PDF-conversion tests still assuming ImageMagick instead
  of the current PyMuPDF-first path. Drop test_container.py (obsolete
  Docker-container smoke tests, fully superseded elsewhere).
- Add a plain-venv + systemd --user timer deployment path
  (deploy/systemd/) for HPC login nodes without a Docker daemon, where
  public_html is already served by existing infrastructure.
- Document both in CLAUDE.md, including running CI's checks locally
  before committing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plotstyle/style.py

@@ -20,10 +20,10 @@ exactly this reason.
 
 from __future__ import annotations
 
-from cycler import cycler
 from importlib import resources
 
 import matplotlib.pyplot as plt
+from cycler import cycler
 
 from .colors import CATEGORICAL
 
@@ -45,7 +45,7 @@ def use(cycle_linestyles: bool = False) -> None:
     sequence, so series stay distinguishable even if color is lost
     (grayscale printing, projector glare, color-vision deficiency).
     """
-    style_path = resources.files("plotstyle").joinpath("assets", "plotstyle.mplstyle")
+    style_path = resources.files("plotstyle").joinpath("assets").joinpath("plotstyle.mplstyle")
     plt.style.use(str(style_path))
 
     if cycle_linestyles: