Add hub-core package, docs, and State Hub integration scaffold

Extract the first reusable slice (models, schemas, routers, MCP, migrations)
from state-hub with INTENT/SCOPE, agent instructions, workplan, and aligned
inter_hub capability registry index.

tests/test_mcp.py

@@ -0,0 +1,31 @@
+import asyncio
+
+from hub_core.mcp import HubCoreMCPServer
+
+
+def test_mcp_base_server_constructs_without_registering_tools() -> None:
+    server = HubCoreMCPServer(
+        name="test-hub",
+        api_base="http://127.0.0.1:9999/",
+        register_tools=False,
+    )
+
+    assert server.api_base == "http://127.0.0.1:9999"
+    assert server.mcp.name == "test-hub"
+    assert server._clean({"a": None, "b": 1}) == {"b": 1}
+
+
+def test_mcp_base_server_registers_orientation_doi_and_fos10_tools() -> None:
+    server = HubCoreMCPServer(name="test-hub", api_base="http://127.0.0.1:9999")
+
+    tools = asyncio.run(server.mcp.list_tools())
+    names = {tool.name for tool in tools}
+
+    assert {
+        "get_state_summary",
+        "get_domain_summary",
+        "check_repo_doi",
+        "get_doi_summary",
+        "get_risks",
+        "get_alerts",
+    } <= names