feat: implement comprehensive PWA force update system

- Add UpdateManager and UpdateChecker for automatic version detection
- Add post-build script for meta.json generation and version injection
- Enhance Service Worker with version-aware caching
- Add .htaccess configuration for proper cache control

This ensures all users receive the latest version after deployment
without manual cache clearing.

manifest.json

@@ -1,5 +1,5 @@
 {
-  "name": "SecureBit.chat v4.7.53 - ECDH + DTLS + SAS",
+  "name": "SecureBit.chat v4.7.55 - ECDH + DTLS + SAS",
   "short_name": "SecureBit",
   "description": "P2P messenger with ECDH + DTLS + SAS security, military-grade cryptography and Lightning Network payments",
   "start_url": "./",