ui: grey out other upgrade arrows while host update runs (0.4.0)

Show inactive grey arrows on other hosts during a single remote agent update; bump SAC to 0.4.0.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/version.ts

@@ -1,4 +1,4 @@
 /** Fallback до загрузки /health; при релизе держите в sync с backend/app/version.py */
 export const APP_NAME = "Security Alert Center";
-export const APP_VERSION = "0.3.8";
+export const APP_VERSION = "0.4.0";
 export const APP_VERSION_LABEL = `${APP_NAME} v.${APP_VERSION}`;