refactor: improve editor and cuesheet headers

- consistent behaviour for app mode
- improve navigation

apps/client/src/ontimeConfig.ts

@@ -4,3 +4,13 @@ export const tooltipDelayFast = 300;
 
 export const queryRefetchInterval = 60000; // 60 seconds
 export const queryRefetchIntervalSlow = 120000; // 120 seconds
+
+export const sessionKeys = {
+  cuesheetMode: 'cuesheet-mode',
+  editorMode: 'editor-mode',
+};
+
+export enum AppMode {
+  Run = 'run',
+  Edit = 'edit',
+}