Add list_images and delete_image tools (Gruppe 1)

- list_images: lists all local Docker images sorted by size desc,
  shows size (human-readable), creation date, in-use marker, and
  update-available marker; gracefully handles container list failure
- delete_image: accepts name:tag or image hash, blocks deletion when
  image is in use by a container, requires confirmed=True to execute;
  default shows a dry-run preview
- 16 unit tests covering all paths (mock DSM client)
- ruff format + check clean

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -37,3 +37,8 @@ select = ["E", "F", "W", "I", "N", "UP", "B", "SIM", "TCH"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
+
+[dependency-groups]
+dev = [
+    "ruff>=0.15.10",
+]