chore: release SAC 0.5.0

Bump version, document security hardening in README, add github snapshot
push script with URL/login/IP sanitization for public mirror.

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 = "0.4.15";
+export const APP_VERSION = "0.5.0";
 export const APP_VERSION_LABEL = `${APP_NAME} v.${APP_VERSION}`;