feat(auth): drop test-client defaults, add ALLOWED_MGMT_CLIENT allowlist

Both auth surfaces now fail-closed by default:

- ALLOWED_MCP_CLIENTS: removed the silent `claude-desktop` and
  `test-mcp-client` fallbacks. Empty/unset env var leaves the registry
  empty so /oauth/authorize rejects every client_id.
- ALLOWED_MGMT_CLIENT (new): comma-separated list of OIDC client_ids
  whose tokens are accepted by /api/management/*. Enforced in
  verify_token_for_management_api on both the cache-hit and cache-miss
  paths against the token's client_id claim. Unset/empty rejects all.

Compose: set ALLOWED_MGMT_CLIENT=nextcloudMcpServerUIPublicClient on
mcp-multi-user-basic so the existing Astrolabe integration test
(test_astrolabe_chunk_context.py) still passes.

env.sample documents both vars and notes they may be consolidated later.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/test_client_registry.py

@@ -88,20 +88,23 @@ def test_http_non_localhost_rejected(monkeypatch, caplog):
     assert "evil.com" in caplog.text
 
 
-def test_empty_string_uses_well_known(monkeypatch):
-    registry = _get_registry(monkeypatch, "")
-    clients = registry.list_clients()
-    client_ids = {c.client_id for c in clients}
-    assert "claude-desktop" in client_ids
-    assert "test-mcp-client" in client_ids
+def test_empty_string_yields_empty_registry(monkeypatch, caplog):
+    with caplog.at_level(logging.WARNING):
+        registry = _get_registry(monkeypatch, "")
+    assert registry.list_clients() == []
+    valid, err = registry.validate_client("claude-desktop")
+    assert valid is False
+    assert "Unknown client_id" in err
+    assert "ALLOWED_MCP_CLIENTS is unset or empty" in caplog.text
 
 
-def test_unset_env_uses_well_known(monkeypatch):
-    registry = _get_registry(monkeypatch, None)
-    clients = registry.list_clients()
-    client_ids = {c.client_id for c in clients}
-    assert "claude-desktop" in client_ids
-    assert "test-mcp-client" in client_ids
+def test_unset_env_yields_empty_registry(monkeypatch, caplog):
+    with caplog.at_level(logging.WARNING):
+        registry = _get_registry(monkeypatch, None)
+    assert registry.list_clients() == []
+    valid, err = registry.validate_client("test-mcp-client")
+    assert valid is False
+    assert "Unknown client_id" in err
 
 
 def test_malformed_entries_skipped_with_warning(monkeypatch, caplog):
@@ -153,14 +156,6 @@ def test_validate_redirect_uri_localhost_wildcard(monkeypatch):
     assert err is None
 
 
-def test_well_known_clients_wildcard_scopes(monkeypatch):
-    registry = _get_registry(monkeypatch, None)
-    for client in registry.list_clients():
-        assert client.allowed_scopes == ["*"], (
-            f"Well-known client {client.client_id} should have wildcard scopes"
-        )
-
-
 def test_client_name_resolution(monkeypatch):
     registry = _get_registry(monkeypatch, "claude-desktop, custom-tool")
     assert registry.get_client("claude-desktop").name == "Claude Desktop"