Add SSE client for web chat integration and enable event-based message handling.

- Introduced `SseSubscribeClient` to connect to the external web server and process events via SSE (Server-Sent Events).
- Added `WebHandler` interface for type-safe event deserialization and processing.
- Included `WebChatHandler` to handle incoming web chat messages and forward them to the chat system.
- Updated `Config` for new configurable values: `CHAT_WEB_REGISTER_TO_BASE_URL` and `CHAT_WEB_TOKEN`.

api/build.gradle.kts

@@ -16,6 +16,7 @@ dependencies {
     //API validation
     implementation("org.hibernate.validator:hibernate-validator:9.0.1.Final")
     implementation("org.glassfish:jakarta.el:5.0.0-M1")
+    implementation("com.fasterxml.jackson.core:jackson-databind:2.22.1")
 }
 
 publishing {