feat: implement complete JSON serialization system with response classes

- Add abstract JsonSerializable base class with toJson/fromJson methods
- Create comprehensive response classes for complete JSON document handling:
  * ClusterMembersResponse for cluster member data
  * TaskStatusResponse and TaskControlResponse for task operations
  * NodeStatusResponse, NodeEndpointsResponse, NodeOperationResponse for node data
- Implement concrete serializable classes for all data types:
  * NodeInfoSerializable, TaskInfoSerializable, SystemInfoSerializable
  * TaskSummarySerializable, EndpointInfoSerializable
- Refactor all service classes to use new serialization system
- Reduce service method complexity from 20-30 lines to 2-3 lines
- Eliminate manual JsonDocument creation and field mapping
- Ensure type safety and compile-time validation
- Maintain backward compatibility while improving maintainability

Breaking change: Service classes now use response objects instead of manual JSON creation

include/spore/util/JsonSerializable.h

@@ -0,0 +1,56 @@
+#pragma once
+#include <ArduinoJson.h>
+
+namespace spore {
+namespace util {
+
+/**
+ * Abstract base class for objects that can be serialized to/from JSON
+ * Provides a clean interface for converting objects to JsonObject and back
+ */
+class JsonSerializable {
+public:
+    virtual ~JsonSerializable() = default;
+    
+    /**
+     * Serialize this object to a JsonObject
+     * @param obj The JsonObject to populate with this object's data
+     */
+    virtual void toJson(JsonObject& obj) const = 0;
+    
+    /**
+     * Deserialize this object from a JsonObject
+     * @param obj The JsonObject containing the data to populate this object
+     */
+    virtual void fromJson(const JsonObject& obj) = 0;
+    
+    /**
+     * Convenience method to create a JsonObject from this object
+     * @param doc The JsonDocument to create the object in
+     * @return A JsonObject containing this object's serialized data
+     */
+    JsonObject toJsonObject(JsonDocument& doc) const {
+        JsonObject obj = doc.to<JsonObject>();
+        toJson(obj);
+        return obj;
+    }
+    
+    /**
+     * Convenience method to create a JsonArray from a collection of serializable objects
+     * @param doc The JsonDocument to create the array in
+     * @param objects Collection of objects implementing JsonSerializable
+     * @return A JsonArray containing all serialized objects
+     */
+    template<typename Container>
+    static JsonArray toJsonArray(JsonDocument& doc, const Container& objects) {
+        JsonArray arr = doc.to<JsonArray>();
+        for (const auto& obj : objects) {
+            JsonObject item = arr.add<JsonObject>();
+            obj.toJson(item);
+        }
+        return arr;
+    }
+};
+
+} // namespace util
+} // namespace spore