Fix ConnectionEdit silently NULLing out port references

The edit handler was fetching the connection twice but never using the
result, then constructing a new Connection struct without PortID1/PortID2
fields. The DB update would write NULL into both port columns, severing
the cable from both ends. Now the handler fetches the existing row once
and updates only the submitted metadata fields in place.

internal/handlers/connections.go

@@ -50,41 +50,43 @@ func (h *Handlers) ConnectionEdit(w http.ResponseWriter, r *http.Request) {
 	id, _ := strconv.ParseInt(idStr, 10, 64)
 	r.ParseForm()
 
-	_, err := h.Store.ConnectionGetByID(id)
-	if err != nil {
+	conn, err := h.Store.ConnectionGetByID(id)
+	if err != nil || conn == nil {
 		http.Error(w, "connection not found", http.StatusNotFound)
 		return
 	}
 
-	connTypeID, _ := strconv.ParseInt(r.FormValue("connection_type_id"), 10, 64)
+	if ctStr := r.FormValue("connection_type_id"); ctStr != "" {
+		ctID, err := strconv.ParseInt(ctStr, 10, 64)
+		if err == nil && ctID > 0 {
+			conn.ConnectionTypeID = ctID
+		}
+	}
+
 	label1 := r.FormValue("label_1")
-	label2 := r.FormValue("label_2")
-	color := r.FormValue("color")
-	returnPortID := r.FormValue("return_port_id")
-
-	if color == "" {
-		color = "#808080"
-	}
-
-	var label1Ptr, label2Ptr *string
 	if label1 != "" {
-		label1Ptr = &label1
+		conn.Label1 = &label1
+	} else {
+		conn.Label1 = nil
 	}
+
+	label2 := r.FormValue("label_2")
 	if label2 != "" {
-		label2Ptr = &label2
+		conn.Label2 = &label2
+	} else {
+		conn.Label2 = nil
 	}
 
-	_, err = h.Store.ConnectionGetByID(id)
-	if err == nil {
-		_ = h.Store.ConnectionUpdate(&models.Connection{
-			ID:               id,
-			ConnectionTypeID: connTypeID,
-			Label1:           label1Ptr,
-			Label2:           label2Ptr,
-			Color:            color,
-		})
+	if color := r.FormValue("color"); color != "" {
+		conn.Color = color
 	}
 
+	if err := h.Store.ConnectionUpdate(conn); err != nil {
+		http.Error(w, "Failed to update connection", http.StatusInternalServerError)
+		return
+	}
+
+	returnPortID := r.FormValue("return_port_id")
 	if returnPortID != "" {
 		h.renderConnectionModal(w, returnPortID)
 		return