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/slugs.py

@@ -0,0 +1,14 @@
+import re
+
+_NON_SLUG = re.compile(r"[^a-z0-9]+")
+_DASHES = re.compile(r"-+")
+
+
+def slugify(value: str, *, max_length: int = 100) -> str:
+    slug = _NON_SLUG.sub("-", value.strip().lower())
+    slug = _DASHES.sub("-", slug).strip("-")
+    if not slug:
+        raise ValueError("slug cannot be empty")
+    if max_length < 1:
+        raise ValueError("max_length must be >= 1")
+    return slug[:max_length].strip("-")