docs: add agent skill guides and update CMake build instructions

.agents/skills/core_system.md

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+# Skill: Core Object & Property System
+
+This skill defines the patterns for implementing and working with the `uLib` core object model.
+
+## Context
+- **Base Class**: `uLib::Object`
+- **Property System**: `uLib::Property<T>`
+- **Registration**: All objects must register their properties for UI visibility and serialization.
+
+## Implementation Patterns
+
+### 1. Defining an Object
+Inherit from `uLib::Object` and use the `ULIB_PROPERTY` macro for members.
+```cpp
+class MyObject : public uLib::Object {
+public:
+    ULIB_PROPERTY(double, Speed, 0.0)
+    ULIB_PROPERTY(std::string, Description, "None")
+    
+    MyObject() {
+        // Required for property visibility in PropertyEditor
+        ULIB_ACTIVATE_PROPERTIES(*this)
+    }
+};
+```
+
+### 2. Property Access
+Properties can be treated like their underlying types or accessed via `.Get()`/`.Set()`.
+```cpp
+obj.Speed = 10.5;                // Triggers Updated() signal
+double s = obj.Speed;            // Implicit conversion
+obj.Speed.SetRange(0.0, 100.0);  // Setting metadata
+```
+
+### 3. Serialization
+Implement `serialize` overloads for different archive types. Use `hrp` (Human Readable Property) to name fields.
+```cpp
+template <class ArchiveT>
+void serialize(ArchiveT &ar, const unsigned int version) {
+    ar & boost::serialization::make_nvp("InstanceName", this->GetInstanceName());
+    ar & boost::serialization::make_hrp("Speed", Speed, "m/s");
+}
+```
+
+## Checklist
+- [ ] Inherit from `uLib::Object`.
+- [ ] Use `ULIB_PROPERTY` for members that should appear in the GUI.
+- [ ] Call `ULIB_ACTIVATE_PROPERTIES` in the constructor.
+- [ ] Implement `serialize` if persistence is required.