dashboard: lifecycle_action helper collapses start/stop/restart/rebuild

five POST handlers (post_kill / post_restart / post_start / post_rebuild)
were all repeating the same boilerplate: strip prefix, set_transient,
call lifecycle::X, clear_transient, match the result. extract one
helper that takes the transient kind, error-message verb, the work
body, and an optional 'on success' tail (used by kill to also
unregister + emit HelperEvent::Killed). each handler shrinks to a
single lifecycle_action(..) call. zero behavior change.

hive-ag3nt/src/events.rs

@@ -114,7 +114,6 @@ impl EventStore {
         out.reverse();
         Ok(out)
     }
-
 }
 
 #[derive(Clone)]
@@ -172,7 +171,6 @@ impl Bus {
         };
         store.recent(HISTORY_CAPACITY).unwrap_or_default()
     }
-
 }
 
 impl Default for Bus {