Add HealthChat API and extended profile services (#9)

Expose OpenID tokens and homeserver credentials from the client proxy, and
add fork-only services for the HealthChat member directory backend
(api.healthchat.ch) plus a service that reads MSC4133 extended profile
fields directly from the homeserver. Groundwork for the members tab and
the profile screens.

Claude-Session: https://claude.ai/code/session_013qdTbAWsZj2quQzEkagXaS

ElementX/Sources/Services/Client/ClientProxy.swift

@@ -838,6 +838,28 @@ class ClientProxy: ClientProxyProtocol {
         }
     }
     
+    func requestOpenIDToken() async -> Result<OpenIDToken, ClientProxyError> {
+        do {
+            return try await .success(.init(rustValue: client.requestOpenidToken()))
+        } catch {
+            MXLog.error("Failed requesting OpenID token with error: \(error)")
+            return .failure(.sdkError(error))
+        }
+    }
+    
+    func homeserverCredentials() -> Result<HomeserverCredentials, ClientProxyError> {
+        do {
+            let session = try client.session()
+            guard let homeserverURL = URL(string: session.homeserverUrl) else {
+                return .failure(.invalidServerName)
+            }
+            return .success(.init(homeserverURL: homeserverURL, accessToken: session.accessToken))
+        } catch {
+            MXLog.error("Failed retrieving the session's credentials with error: \(error)")
+            return .failure(.sdkError(error))
+        }
+    }
+    
     func roomDirectorySearchProxy() -> RoomDirectorySearchProxyProtocol {
         RoomDirectorySearchProxy(roomDirectorySearch: client.roomDirectorySearch())
     }