feat(cli): add open-reuse validate and register portfolio integrations

Implement Integration Definition validator CLI with schema and index checks,
pytest suite, and CI workflow. Register open-cmis-tck and issue-core-gitea in
the integration index.

Closes OPEN-WP-0003 and OPEN-WP-0004.

open_reuse/registry.py

@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any
+
+import yaml
+
+PACKAGE_ROOT = Path(__file__).resolve().parent.parent
+
+INDEX_REQUIRED_FIELDS = (
+    "id",
+    "name",
+    "status",
+    "owner",
+    "reuse_mode",
+    "path",
+    "repo",
+    "upstream",
+)
+
+
+def resolve_repo_root(root: Path | None = None) -> Path:
+    if root is not None:
+        return root.resolve()
+    candidate = PACKAGE_ROOT
+    markers = (
+        candidate / "schemas" / "integration.schema.yaml",
+        candidate / "registry" / "indexes" / "integrations.yaml",
+    )
+    if all(path.exists() for path in markers):
+        return candidate
+    raise FileNotFoundError(
+        "Could not resolve open-reuse repo root; pass --root explicitly."
+    )
+
+
+def registry_paths(repo_root: Path) -> dict[str, Path]:
+    registry = repo_root / "registry"
+    return {
+        "registry": registry,
+        "integrations": registry / "integrations",
+        "index": registry / "indexes" / "integrations.yaml",
+        "schema": repo_root / "schemas" / "integration.schema.yaml",
+    }
+
+
+def load_schema(repo_root: Path) -> dict[str, Any]:
+    schema_path = registry_paths(repo_root)["schema"]
+    with schema_path.open(encoding="utf-8") as handle:
+        return yaml.safe_load(handle)
+
+
+def load_yaml(path: Path) -> dict[str, Any]:
+    with path.open(encoding="utf-8") as handle:
+        data = yaml.safe_load(handle)
+    if not isinstance(data, dict):
+        raise ValueError(f"{path}: expected YAML mapping at root")
+    return data
+
+
+def load_index(repo_root: Path) -> dict[str, Any]:
+    index_path = registry_paths(repo_root)["index"]
+    if not index_path.exists():
+        return {"integrations": []}
+    return load_yaml(index_path)
+
+
+def integration_paths(repo_root: Path, targets: list[Path] | None = None) -> list[Path]:
+    if targets:
+        return [path.resolve() for path in targets]
+    integrations_dir = registry_paths(repo_root)["integrations"]
+    if not integrations_dir.exists():
+        return []
+    return sorted(
+        path
+        for path in integrations_dir.glob("*.integration.yaml")
+        if path.is_file()
+    )
+
+
+def resolve_external_definition(
+    repo_slug: str,
+    relative_path: str,
+    repos_base: Path | None,
+) -> Path | None:
+    if repos_base is None:
+        return None
+    candidate = (repos_base / repo_slug / relative_path).resolve()
+    if candidate.is_file():
+        return candidate
+    return None