chore(deps): update tokio-tungstenite requirement in /veza-chat-server

Updates the requirements on [tokio-tungstenite](https://github.com/snapview/tokio-tungstenite) to permit the latest version.
- [Changelog](https://github.com/snapview/tokio-tungstenite/blob/master/CHANGELOG.md)
- [Commits](https://github.com/snapview/tokio-tungstenite/compare/v0.21.0...v0.28.0)

---
updated-dependencies:
- dependency-name: tokio-tungstenite
  dependency-version: 0.28.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

veza-chat-server/Cargo.toml

@@ -31,7 +31,7 @@ tokio = { version = "1.35", features = [
     "tracing",       # Support tracing
     "signal",        # Signaux système pour shutdown gracieux
 ] }
-tokio-tungstenite = "0.21"      # WebSocket server/client
+tokio-tungstenite = "0.28"      # WebSocket server/client
 tungstenite = "0.21"            # Core WebSocket
 futures-util = "0.3"            # Utilitaires futures
 hyper = { version = "1.0", features = ["full"] }  # Client HTTP pour webhooks