add freeze feature to rundown (#1106)

* add frozen flag to runtime store

* add middleware for when frozen

* prevent rundown editing when frozen

* add endpoint to router to set frozen state

* add frozen property to rundown placeholder in client

apps/client/src/common/stores/runtime.ts

@@ -48,6 +48,7 @@ export const runtimeStorePlaceholder: RuntimeStore = {
     duration: 0,
     playback: SimplePlayback.Stop,
   },
+  frozen: false,
 };
 
 const deepCompare = <T>(a: T, b: T) => isEqual(a, b);