Implement REUSE-WP-0013 registry establish, update, and stats

Add stats, establish (scaffold, publish-check, discover), and update CLI
commands with optional llm-connect bridge, validate --root for sibling repos,
pytest coverage, and documentation for sibling registry onboarding.

reuse_surface/registry.py

@@ -60,4 +60,31 @@ def parse_vector(vector: str) -> dict[str, str]:
 
 def level_at_least(dimension: str, current: str, minimum: str) -> bool:
     order = LEVEL_ORDERS[dimension]
-    return order.index(current) >= order.index(minimum)
+    return order.index(current) >= order.index(minimum)
+
+
+def registry_paths(repo_root: Path) -> dict[str, Path]:
+    registry = repo_root / "registry"
+    return {
+        "registry": registry,
+        "capabilities": registry / "capabilities",
+        "index": registry / "indexes" / "capabilities.yaml",
+        "sources": registry / "federation" / "sources.yaml",
+    }
+
+
+def load_index_at(path: Path) -> dict[str, Any]:
+    with path.open(encoding="utf-8") as handle:
+        return yaml.safe_load(handle)
+
+
+def entry_vector(front_matter: dict[str, Any]) -> str:
+    discovery = front_matter["maturity"]["discovery"]["current"]
+    availability = front_matter["maturity"]["availability"]["current"]
+    completeness = front_matter["external_evidence"]["completeness"]["level"]
+    reliability = front_matter["external_evidence"]["reliability"]["level"]
+    return f"{discovery} / {availability} / {completeness} / {reliability}"
+
+
+def vectors_match(index_vector: str, front_matter: dict[str, Any]) -> bool:
+    return index_vector.replace(" ", "") == entry_vector(front_matter).replace(" ", "")