refactor: consolidate skill docs, add anti-drift tests, and apply audit fixes

DLO-13: Restructure vlm-library-workflow skill as safety contract layer.
- Rewrite SKILL.md (69 lines): safety contract, execution threshold semantics,
  six-step high-risk loop, decision rules, phase skeleton
- Delete redundant references (cli-reference, workflow, command-recipes, dev-guide)
- Add triage.md (failure mapping + preflight) and dev-map.md (module→test mapping)
- Add tests/test_docs_consistency.py: 78 parametrized tests verifying documented
  vlm commands exist in CLI registry
- Add CSV path mismatch test to test_plan_review.py (4th safety gate path)
- Delete vlm-expert.skill (Gemini package, 7 months stale) and README Gemini section

DLO-2 audit fixes: rate limiter injection, symmetric quarantine categories,
review-plan safety gates, parser improvements, planner validation.

CLI modularization: commands/ directory with one module per command group.

src/vlm/scanner.py

@@ -290,6 +290,56 @@ def _is_video_file(file_path: Path, video_extensions: list[str]) -> bool:
     return file_extension in [ext.lower() for ext in video_extensions]
 
 
+DEFAULT_SIDECAR_EXTENSIONS = (".srt", ".ass", ".sub", ".idx", ".sup", ".nfo")
+
+
+def find_sidecar_companions(
+    video_path: Path,
+    sidecar_extensions: tuple = DEFAULT_SIDECAR_EXTENSIONS,
+) -> list[Path]:
+    """Find sidecar files in the same directory that belong to a video file.
+
+    Conservative matching: a companion must share the video's exact stem,
+    optionally followed by dot-separated alphabetic suffix tokens (e.g.
+    language or track tags such as ``zh`` or ``en.forced``). Numeric or
+    otherwise non-alphabetic tokens are rejected so unrelated files are
+    never associated.
+
+    Args:
+        video_path: Path to the video file
+        sidecar_extensions: Sidecar extensions to consider (case-insensitive)
+
+    Returns:
+        Sorted list of companion paths (empty when none are found).
+    """
+    parent = video_path.parent
+    try:
+        with os.scandir(parent) as it:
+            entries = [e for e in it if e.is_file(follow_symlinks=False)]
+    except OSError:
+        return []
+
+    stem = video_path.stem
+    exts = {ext.lower() for ext in sidecar_extensions}
+    companions: list[Path] = []
+    for entry in entries:
+        name = entry.name
+        suffix = Path(name).suffix.lower()
+        if suffix not in exts:
+            continue
+        base = name[: -len(suffix)]
+        if base == stem:
+            companions.append(Path(entry.path))
+            continue
+        if not base.startswith(stem + "."):
+            continue
+        tokens = base[len(stem) + 1:].split(".")
+        if tokens and all(token and token.isalpha() for token in tokens):
+            companions.append(Path(entry.path))
+
+    return sorted(companions, key=lambda p: p.name)
+
+
 def _create_video_file(
     file_path: Path,
     library_root: Path,