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/cli.py

@@ -0,0 +1,74 @@
+from __future__ import annotations
+
+import argparse
+import sys
+from pathlib import Path
+
+from open_reuse.validate import run_validate
+
+
+def _build_parser() -> argparse.ArgumentParser:
+    parser = argparse.ArgumentParser(prog="open-reuse")
+    subparsers = parser.add_subparsers(dest="command", required=True)
+
+    validate = subparsers.add_parser(
+        "validate",
+        help="Validate integration definitions and registry index",
+    )
+    validate.add_argument(
+        "paths",
+        nargs="*",
+        type=Path,
+        help="Integration definition files (default: registry/integrations/*.integration.yaml)",
+    )
+    validate.add_argument(
+        "--root",
+        type=Path,
+        default=None,
+        help="open-reuse repository root (auto-detected when omitted)",
+    )
+    validate.add_argument(
+        "--repos-base",
+        type=Path,
+        default=None,
+        help="Base directory containing consuming repos for external definition checks",
+    )
+    validate.add_argument(
+        "--no-index",
+        action="store_true",
+        help="Skip indexes/integrations.yaml checks",
+    )
+    validate.add_argument(
+        "--indexed-only",
+        action="store_true",
+        help="When checking index, skip local definition drift warnings",
+    )
+    validate.add_argument(
+        "--fail-on-warnings",
+        action="store_true",
+        help="Exit non-zero when promotion-gate warnings are present",
+    )
+    return parser
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = _build_parser()
+    args = parser.parse_args(argv)
+
+    if args.command == "validate":
+        targets = args.paths or None
+        return run_validate(
+            root=args.root,
+            targets=targets,
+            repos_base=args.repos_base,
+            fail_on_warnings=args.fail_on_warnings,
+            check_index=not args.no_index,
+            indexed_only=args.indexed_only,
+        )
+
+    parser.error(f"unknown command: {args.command}")
+    return 2
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())