release: v4.8.9 security hardening patch

- upgrade DOMPurify to patched release (fixes high-severity XSS GHSA-87xg-pxx2-7hvx)
- upgrade esbuild build dependency; npm audit now reports 0 vulnerabilities
- stop tracking config/ice-servers.js (TURN credentials); add example template
- production logger no longer prints error context or info/debug output
- bump version to 4.8.9 across header, manifest, README, init message
- update SECURITY.md supported-release table to v4.8.x

dist/app.js

@@ -1820,7 +1820,7 @@ var EnhancedSecureP2PChat = () => {
       } catch (error) {
       }
     }
-    handleMessage(" SecureBit.chat Enhanced Security Edition v4.8.7 - ECDH + DTLS + SAS initialized. Ready to establish a secure connection with ECDH key exchange, DTLS fingerprint verification, and SAS authentication to prevent MITM attacks.", "system");
+    handleMessage(" SecureBit.chat Enhanced Security Edition v4.8.9 - ECDH + DTLS + SAS initialized. Ready to establish a secure connection with ECDH key exchange, DTLS fingerprint verification, and SAS authentication to prevent MITM attacks.", "system");
     const handleBeforeUnload = (event) => {
       if (event.type === "beforeunload" && !isTabSwitching) {
         if (webrtcManagerRef.current && webrtcManagerRef.current.isConnected()) {