docs: add agent skill guides and update CMake build instructions

.agents/skills/memory_management.md

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+# Skill: Memory Management & Object Lifecycle
+
+This skill provides guidelines for managing memory safely within the `uLib` framework to prevent memory corruption and leaks.
+
+## Context
+- **Ownership**: `ObjectsContext` typically owns its children.
+- **Shared Access**: Use `SmartPointer<T>` for objects shared across multiple systems (e.g., Geant4 and VTK).
+- **Core Principle**: Avoid manual `delete` on objects managed by the framework.
+
+## Patterns
+
+### 1. Context Ownership
+When an object is added to an `ObjectsContext`, it is managed by that context.
+```cpp
+auto* context = new ObjectsContext();
+auto* obj = new MyObject();
+context->AddObject(obj); 
+// Do NOT delete obj; it will be deleted when context is destroyed.
+```
+
+### 2. Smart Pointers
+Use `SmartPointer<T>` for resources like `Material` or `Solid` that are used by both domain logic and external engines (Geant4).
+```cpp
+uLib::SmartPointer<Material> mat = new Material("Lead");
+solid->SetMaterial(mat); // Shared ownership
+```
+
+### 3. Geant4 Object Safety
+Geant4 often takes ownership of certain objects (like `G4VPhysicalVolume`). When wrapping these:
+- Ensure the wrapper doesn't double-free the Geant4-owned pointer.
+- Use `recursion_guard` if synchronizing transformations between `uLib::Object` and Geant4 volumes to prevent signal loops.
+
+## Debugging Memory Issues
+- **SIGABRT (invalid pointer)**: Usually caused by deleting an object that was already managed (and deleted) by an `ObjectsContext` or `SmartPointer`.
+- **Leaks**: Check if objects were created but never added to a context or wrapped in a `SmartPointer`.
+
+## Checklist
+- [ ] Are objects added to an `ObjectsContext`?
+- [ ] Is `SmartPointer` used for shared resources?
+- [ ] Is there a risk of double-freeing Geant4-managed pointers?