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/events.py

@@ -0,0 +1,37 @@
+"""Canonical event types for reusable FOS hub progress streams."""
+
+RISK_SURFACED = "risk_surfaced"
+RISK_MITIGATED = "risk_mitigated"
+RISK_ESCALATED = "risk_escalated"
+
+ALERT_RAISED = "alert_raised"
+ALERT_ACKNOWLEDGED = "alert_acknowledged"
+ALERT_RESOLVED = "alert_resolved"
+
+RISK_EVENT_TYPES = frozenset(
+    {
+        RISK_SURFACED,
+        RISK_MITIGATED,
+        RISK_ESCALATED,
+    }
+)
+ALERT_EVENT_TYPES = frozenset(
+    {
+        ALERT_RAISED,
+        ALERT_ACKNOWLEDGED,
+        ALERT_RESOLVED,
+    }
+)
+FOS10_EVENT_TYPES = RISK_EVENT_TYPES | ALERT_EVENT_TYPES
+
+__all__ = [
+    "ALERT_ACKNOWLEDGED",
+    "ALERT_EVENT_TYPES",
+    "ALERT_RAISED",
+    "ALERT_RESOLVED",
+    "FOS10_EVENT_TYPES",
+    "RISK_ESCALATED",
+    "RISK_EVENT_TYPES",
+    "RISK_MITIGATED",
+    "RISK_SURFACED",
+]