feat: add Highgo (瀚高) database support

Add full support for Highgo database, a PostgreSQL-compatible Chinese
domestic database. Includes database type definition, connection dialog,
agent driver mapping, and database icon.

src-tauri/src/commands/agents.rs

@@ -17,6 +17,7 @@ static REGISTRY_CACHE: std::sync::LazyLock<Mutex<Option<(std::time::Instant, Age
 const AGENT_TYPES: &[(&str, &str)] = &[
     ("dameng", "达梦 DM8"),
     ("kingbase", "人大金仓 KingbaseES"),
+    ("highgo", "瀚高 HighGo"),
     ("vastbase", "Vastbase"),
     ("goldendb", "GoldenDB"),
     ("oracle", "Oracle"),

src-tauri/src/commands/connection.rs

@@ -164,6 +164,9 @@ pub async fn connect_db(state: State<'_, Arc<AppState>>, config: ConnectionConfi
     let id = config.id.clone();
     let db_config = metadata_connection_config(&config);
 
+    state.remove_connection_pools(&id).await;
+    state.reset_connection_transport(&id).await;
+
     let (host, port) = state.connection_host_port(&id, &db_config).await?;
     probe_connection_endpoint(&db_config, &host, port).await?;
     let url = connection_url_for_endpoint(&db_config, &host, port);
@@ -287,7 +290,6 @@ pub async fn disconnect_db(state: State<'_, Arc<AppState>>, connection_id: Strin
     }
     drop(conns);
     state.configs.write().await.remove(&connection_id);
-    state.tunnels.stop_tunnel(&connection_id).await;
-    state.proxy_tunnels.stop_tunnel(&connection_id).await;
+    state.reset_connection_transport(&connection_id).await;
     Ok(())
 }