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.

tests/test_establish.py

@@ -0,0 +1,77 @@
+from __future__ import annotations
+
+from pathlib import Path
+from unittest.mock import patch
+
+import yaml
+
+from reuse_surface.establish import (
+    discover_capabilities,
+    publish_check,
+    scaffold_registry,
+)
+from reuse_surface.registry import registry_paths
+
+
+def test_scaffold_creates_layout(tmp_path: Path):
+    created = scaffold_registry(tmp_path, domain="helix_forge")
+    paths = registry_paths(tmp_path)
+    assert paths["index"] in created
+    data = yaml.safe_load(paths["index"].read_text(encoding="utf-8"))
+    assert data["capabilities"] == []
+    assert data["domain"] == "helix_forge"
+
+
+def test_scaffold_refuses_existing_without_force(tmp_path: Path):
+    scaffold_registry(tmp_path)
+    try:
+        scaffold_registry(tmp_path)
+        raise AssertionError("expected ValueError")
+    except ValueError as exc:
+        assert "already exists" in str(exc)
+
+
+def test_publish_check_local_index(tmp_path: Path):
+    scaffold_registry(tmp_path)
+    result = publish_check(tmp_path)
+    assert result["ok"] is True
+    assert any(check["name"] == "local_index_yaml" for check in result["checks"])
+
+
+def test_publish_check_raw_url_fail(tmp_path: Path):
+    with patch(
+        "reuse_surface.establish._probe_raw_url",
+        return_value={"ok": False, "status": 303, "content_type": "text/html"},
+    ):
+        result = publish_check(
+            tmp_path,
+            raw_url="https://example.com/capabilities.yaml",
+        )
+    assert result["ok"] is False
+    assert result.get("remediation")
+
+
+def test_discover_dry_run_mock_llm(tmp_path: Path):
+    scaffold_registry(tmp_path)
+    (tmp_path / "README.md").write_text("# Demo service\n", encoding="utf-8")
+    draft = {
+        "domain": "helix_forge",
+        "capabilities": [
+            {
+                "id": "capability.demo.sample",
+                "name": "Sample",
+                "summary": "Sample capability.",
+                "owner": "demo",
+                "vector": "D2 / A0 / C0 / R0",
+                "tags": ["demo"],
+                "consumption_modes": ["informational"],
+                "discovery_intent": "Enable demo planning.",
+            }
+        ],
+    }
+    with patch(
+        "reuse_surface.establish.request_registry_draft",
+        return_value=draft,
+    ):
+        result = discover_capabilities(tmp_path, dry_run=True, apply=False)
+    assert result["draft"]["capabilities"][0]["id"] == "capability.demo.sample"