feat: replace SSE client with direct TCP/WiFi connection

- Remove SseClientService and ConnectionMode.sseClient
- Add ConnectionMode.tcp with MeshCoreTcpService (port 5000)
- NetworkScannerService: scan TCP port 5000 via raw Socket.connect
- mDNS service type changed to _meshcore._tcp
- connection_dialog: connect via connectTcp() instead of connectToSseServer()
- home_screen: show WiFi icon and label for TCP mode
- Bump meshcore_client to pick up TCP transport support

pubspec.lock

@@ -883,7 +883,7 @@ packages:
     description:
       path: "."
       ref: main
-      resolved-ref: "624e3d3cf6ea32d8245cc85d5b599f30ca910501"
+      resolved-ref: d6f91774f19136ff71b0087feaf95fa5490524d9
       url: "https://github.com/dz0ny/meshcore_client.git"
     source: git
     version: "0.1.0"