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.

pyproject.toml

@@ -0,0 +1,23 @@
+[project]
+name = "hub-core"
+version = "0.1.0"
+description = "Reusable core primitives for FOS hubs"
+requires-python = ">=3.12"
+dependencies = [
+    "fastapi>=0.115.0",
+    "fastmcp>=2.0.0",
+    "httpx>=0.28.0",
+    "sqlalchemy[asyncio]>=2.0.0",
+    "pydantic>=2.10.0",
+]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.hatch.build.targets.wheel]
+packages = ["hub_core"]
+artifacts = ["hub_core/migrations/script.py.mako"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]