docs(notes): add mental model kubernetes responsibility hierarchy

Author: wendev27

mental-models/mental-model-kubernetes-responsibility-hierarchy.md

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+# Kubernetes Responsibility Hierarchy
+
+Think of Kubernetes as a chain of responsibility. Every layer has exactly one job.
+
+```
+You
+│
+▼
+Deployment
+"I want 3 Pods."
+│
+▼
+ReplicaSet
+"I will always keep 3 Pods running."
+│
+▼
+Pods
+"I contain one or more containers."
+│
+▼
+Container Runtime (containerd)
+"I start and stop containers."
+│
+▼
+Containers
+"The actual application."
+```
+
+## Responsibilities
+
+- **Deployment** → Declares the desired state and manages updates.
+- **ReplicaSet** → Ensures the desired number of Pods are running.
+- **Pod** → Groups one or more containers that should run together.
+- **Container Runtime** → Starts and stops containers on the node.
+- **Container** → Runs the application code.
+
+## Self-Healing
+
+If a Pod dies:
+
+```
+Desired Pods = 3
+Current Pods = 2
+
+↓
+
+ReplicaSet creates a new Pod
+
+↓
+
+The Pod requests its containers
+
+↓
+
+The container runtime starts them
+
+↓
+
+Current Pods = 3
+```
+
+The ReplicaSet restores the desired state automatically.
+
+## Scaling
+
+When you scale a Deployment:
+
+```
+Replicas: 3
+
+↓
+
+Replicas: 10
+```
+
+The ReplicaSet creates 7 additional Pods, and each Pod starts its required containers through the container runtime.
+
+Kubernetes doesn't directly create containers—it creates Pods. The container runtime is responsible for launching the containers inside those Pods.