refactor: rename CloudEvents extension attributes hub* → central*

Rename extension attributes for consistency with project naming:
- hubschemaversion → centralschemaversion
- hubcategory → centralcategory
- hubseverity → centralseverity

Non-breaking change - no consumers depend on these names yet.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/central/cloudevents_wire.py

@@ -11,27 +11,27 @@ from central.models import Event
 def wrap_event(event: Event, config: Config) -> tuple[dict[str, Any], str]:
     """
     Wrap an Event into a CNCF CloudEvents v1.0 JSON envelope.
-    
+
     Returns:
         A tuple of (envelope_dict, msg_id) where msg_id is the
         CloudEvent id for use as Nats-Msg-Id header.
     """
     # Build CE type: {prefix}.{category}.v1
     ce_type = f"{config.cloudevents.type_prefix}.{event.category}.v1"
-    
+
     # Serialize event data
     event_data = event.model_dump(mode="json")
-    
+
     # Build extension attributes - lowercase, no underscores per CE spec
     extensions: dict[str, Any] = {
-        "hubschemaversion": config.cloudevents.schema_version,
-        "hubcategory": event.category,
+        "centralschemaversion": config.cloudevents.schema_version,
+        "centralcategory": event.category,
     }
-    
-    # Only include hubseverity if severity is present
+
+    # Only include centralseverity if severity is present
     if event.severity is not None:
-        extensions["hubseverity"] = event.severity
-    
+        extensions["centralseverity"] = event.severity
+
     # Create CloudEvent
     ce = CloudEvent(
         attributes={
@@ -44,9 +44,9 @@ def wrap_event(event: Event, config: Config) -> tuple[dict[str, Any], str]:
         },
         data=event_data,
     )
-    
+
     # Build envelope dict from CloudEvent
     envelope: dict[str, Any] = dict(ce.get_attributes())
     envelope["data"] = ce.data
-    
+
     return envelope, event.id