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.

hub_core/utils/routing.py

@@ -0,0 +1,27 @@
+from urllib.parse import SplitResult, urlsplit, urlunsplit
+
+
+def normalize_trailing_slash(path_or_url: str, *, trailing: bool = True) -> str:
+    """Normalize the path component while preserving query and fragment."""
+    if not path_or_url:
+        return "/" if trailing else ""
+
+    parts = urlsplit(path_or_url)
+    path = parts.path or "/"
+    if trailing:
+        normalized_path = path if path.endswith("/") else f"{path}/"
+    elif path == "/":
+        normalized_path = "/"
+    else:
+        normalized_path = path.rstrip("/")
+
+    if parts.scheme or parts.netloc:
+        return urlunsplit(
+            SplitResult(parts.scheme, parts.netloc, normalized_path, parts.query, parts.fragment)
+        )
+    suffix = ""
+    if parts.query:
+        suffix += f"?{parts.query}"
+    if parts.fragment:
+        suffix += f"#{parts.fragment}"
+    return f"{normalized_path}{suffix}"