Replace free TURN with self-hosted coturn; fix Safari connectivity; release v5.4.10

- config/ice-servers.prod.js: swap ExpressTURN for self-hosted coturn at
  turn.securebit.chat (TURN udp/tcp on 3478, TURNS/TLS on 443). Long-lived
  REST-API credential (expiry capped at int32 max for coturn compatibility).
- Add raw-IP STUN/TURN fallback (144.172.96.126): Safari's WebRTC layer fails
  to resolve STUN/TURN hostnames on some networks and gathers no srflx/relay
  candidates; reaching the server by IP fixes cross-browser (Safari<->Chrome)
  connections. Harmless to other browsers.
- deploy/nginx.conf: never long-cache /config/ice-servers.js so clients don't
  lock onto a stale server list.
- Bump version to 5.4.10 (header + init banner).

src/app.jsx

@@ -3447,7 +3447,7 @@ import {
                             }
                         }
 
-                        handleMessage(' SecureBit.chat Enhanced Security Edition v5.4.5 - 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 v5.4.10 - 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');
 
                         // Setup file transfer callbacks (id-bound to THIS session's manager).
                         manager.setFileTransferCallbacks(

src/components/ui/Header.jsx

@@ -559,7 +559,7 @@ const EnhancedMinimalHeader = ({
                     React.createElement('div', { key: 'txt', style: { lineHeight: 1.2, minWidth: 0 } }, [
                         React.createElement('div', { key: 'r1', style: { display: 'flex', alignItems: 'baseline', gap: '7px' } }, [
                             React.createElement('span', { key: 'n', style: { fontSize: '16px', fontWeight: 800, letterSpacing: '-0.3px', color: '#e8e8eb' } }, 'SecureBit'),
-                            React.createElement('span', { key: 'v', style: { fontFamily: MONO, fontSize: '10px', fontWeight: 500, color: '#56565e' } }, 'v5.4.5')
+                            React.createElement('span', { key: 'v', style: { fontFamily: MONO, fontSize: '10px', fontWeight: 500, color: '#56565e' } }, 'v5.4.10')
                         ]),
                         React.createElement('div', { key: 'r2', className: 'hidden sm:block', style: { fontSize: '11px', color: '#6b6b73', fontWeight: 500 } }, 'End-to-end encrypted')
                     ])

src/network/EnhancedSecureWebRTCManager.js

@@ -8644,7 +8644,7 @@ async processMessage(data) {
                         publicKeyType: ecdhKeyPair.publicKey.algorithm?.name,
                         isEphemeral: true
                     });
-                    
+
                 } catch (ecdhError) {
                     this._secureLog('error', 'Ephemeral ECDH key generation failed', {
                         operationId: operationId,