docs(product-console): add v2.4 upgrade guide

charts/product-console/docs/UPGRADE-2.4.md

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+# Helm Upgrade from v2.3.x to v2.4.x
+
+## Topics
+
+- **[Overview](#overview)**
+- **[Features](#features)**
+  - [1. Configurable liveness and readiness probes](#1-configurable-liveness-and-readiness-probes)
+  - [2. Default readiness path changed to /readyz](#2-default-readiness-path-changed-to-readyz)
+- **[Configuration Changes](#configuration-changes)**
+- **[Migration Steps](#migration-steps)**
+- **[Preview changes before upgrading](#preview-changes-before-upgrading)**
+- **[Command to upgrade](#command-to-upgrade)**
+
+## Overview
+
+This is a minor maintenance release that exposes the deployment liveness and readiness probes through `values.yaml` and updates the default readiness path. The application version is unchanged.
+
+| Field | v2.3.x | v2.4.x |
+|-------|--------|--------|
+| Chart version | `2.3.1-beta.1` | `2.4.0-beta.1` |
+| App version | `1.6.0` | `1.6.0` |
+
+## Features
+
+### 1. Configurable liveness and readiness probes
+
+The deployment template now reads probe settings from `values.yaml` instead of using hardcoded values. Two new top-level keys are introduced, both defaulting to `{}` so existing installations keep the same behavior unless overridden.
+
+| Key | v2.3.x | v2.4.x |
+|-----|--------|--------|
+| `livenessProbe` | not present (hardcoded in template) | `{}` (overridable) |
+| `readinessProbe` | not present (hardcoded in template) | `{}` (overridable) |
+
+Each probe block now supports `path`, `initialDelaySeconds`, `periodSeconds`, `timeoutSeconds`, `successThreshold`, and `failureThreshold`. Built-in defaults preserve the prior values for liveness and the prior numeric values for readiness:
+
+```yaml
+# Built-in defaults applied when fields are omitted
+livenessProbe:
+  path: /
+  initialDelaySeconds: 30
+  periodSeconds: 10
+  timeoutSeconds: 5
+  successThreshold: 1
+  failureThreshold: 3
+readinessProbe:
+  path: /readyz
+  initialDelaySeconds: 10
+  periodSeconds: 5
+  timeoutSeconds: 3
+  successThreshold: 1
+  failureThreshold: 3
+```
+
+Example override:
+
+```yaml
+livenessProbe:
+  initialDelaySeconds: 45
+  failureThreshold: 5
+readinessProbe:
+  path: /healthz
+  periodSeconds: 10
+```
+
+### 2. Default readiness path changed to /readyz
+
+The readiness probe HTTP path default has changed from `/` to `/readyz`. The liveness probe default path remains `/`.
+
+| Probe | v2.3.x default | v2.4.x default |
+|-------|----------------|----------------|
+| `livenessProbe.path` | `/` | `/` |
+| `readinessProbe.path` | `/` | `/readyz` |
+
+If the `product-console` application image you deploy does not yet expose `/readyz`, override the path back to `/` in your values:
+
+```yaml
+readinessProbe:
+  path: /
+```
+
+> **Note:** The previous template also did not set `successThreshold`. With v2.4.x, `successThreshold: 1` is now rendered explicitly for both probes, matching Kubernetes defaults.
+
+## Configuration Changes
+
+No existing keys were removed or renamed. The `livenessProbe` and `readinessProbe` blocks are additive and default to `{}`.
+
+| Setting | v2.3.x | v2.4.x | Notes |
+|---------|--------|--------|-------|
+| `livenessProbe` | absent | `{}` | New, optional, overrides built-in defaults |
+| `readinessProbe` | absent | `{}` | New, optional, overrides built-in defaults |
+| `readinessProbe.path` (default) | `/` (hardcoded) | `/readyz` | Override to `/` if your app does not serve `/readyz` |
+
+## Migration Steps
+
+This upgrade requires no mandatory values changes. The Helm upgrade will roll the deployment and update probe paths.
+
+**Recommended upgrade process:**
+
+1. Review the changes using the helm-diff plugin (see [Preview changes before upgrading](#preview-changes-before-upgrading)).
+2. If your image does not expose `/readyz`, set `readinessProbe.path: /` in your values before upgrading.
+3. Run the upgrade command during a maintenance window.
+4. Verify all pods are running and healthy after the upgrade:
+
+```bash
+kubectl get pods -n <namespace>
+```
+
+5. Check service logs for any startup or probe failures:
+
+```bash
+kubectl logs -n <namespace> -l app.kubernetes.io/name=product-console --tail=50
+kubectl describe pod -n <namespace> -l app.kubernetes.io/name=product-console | grep -A2 -E "Liveness|Readiness"
+```
+
+> **Note:** The upgrade triggers a rolling restart of the `product-console` deployment. If the new readiness path returns non-2xx, pods will not become Ready and the rollout will pause.
+
+## Preview changes before upgrading
+
+```bash
+helm diff upgrade product-console oci://registry-1.docker.io/lerianstudio/product-console-helm --version 2.4.0-beta.1 -n <namespace>
+```
+
+> **Note:** Requires the [helm-diff plugin](https://github.com/databus23/helm-diff). Install with: `helm plugin install https://github.com/databus23/helm-diff`
+
+## Command to upgrade
+
+```bash
+helm upgrade product-console oci://registry-1.docker.io/lerianstudio/product-console-helm --version 2.4.0-beta.1 -n <namespace>
+```