refactor(block-h): knowledge retention job lives with plugin; compliance via contract

app/core/job_registry.py

@@ -46,6 +46,15 @@ def get_job(name: str) -> JobFunc | None:
     return _registry.get(name)
 
 
+def unregister_job(name: str) -> None:
+    """Remove a registered job function (plugin deactivation lifecycle).
+
+    Args:
+        name: The job name to remove.
+    """
+    _registry.pop(name, None)
+
+
 def get_all_jobs() -> list[JobFunc]:
     """Return all registered job functions (order is insertion order).