Add Offline Platform install guide (#130)

Signed-off-by: Arnob Kumar Saha <arnob@appscode.com>

Author: ArnobKumarSaha

docs/platform/selfhost-setup/images/acaas-chart.png

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+---
+layout: docs
+menu:
+  docsplatform_{{.version}}:
+    identifier: selfhost-offline-platform
+    name: Offline Platform
+    parent: selfhosted-installer
+    weight: 7
+menu_name: docsplatform_{{.version}}
+section_menu_id: selfhost-setup
+---
+
+# Deploying KubeDB Platform in Offline Mode
+
+This guide describes how to deploy the **KubeDB Platform** in an **offline (air-gapped)** environment. An offline deployment is only supported with the **Self Hosted Production** deployment type — no other deployment type can be installed offline.
+
+In offline mode, AppsCode never receives any of your KubeDB usage data. AppsCode is only involved once, to issue the license against your **Cluster ID** in the very first step. Everything else — including all billing-related functionality — runs entirely inside your own cluster through the **acaas** chart, which is deployed *only* in offline mode.
+
+### Prerequisites
+
+See [Prerequisites](common-config.md#prerequisites) in the Common Configuration guide for the minimum cluster requirements and the optional k3s setup note.
+
+### 1. Visit the KubeDB Platform Self-Hosted Page
+
+Navigate to [KubeDB Platform Self-Hosted](https://appscode.com/selfhost). Here you will find your previously generated self-hosted installers. <br>
+Click on the `Create New Installer` button to get started.
+
+### 2. Choose the Self Hosted Production Deployment Type
+
+Offline mode is only available with the **Self Hosted Production** deployment type. Choose `Deployment Type` -> `Self Hosted Production` and give it a name in the installer name section.
+
+### 3. Enable Offline Installer and Set the Cluster ID
+
+This is the requirement that distinguishes an offline deployment from a standard production deployment.
+
+* Toggle on the **Offline Installer?** option.
+* Set the **Cluster ID** field. This ID is what AppsCode uses to issue the license for your offline cluster. This is the only piece of information AppsCode receives — it is used solely for license issuance.
+
+<br/>
+
+![Offline Toggle](../../images/offline-toggle.png)
+
+> [!NOTE]
+> Because the platform runs fully air-gapped, AppsCode has no visibility into your KubeDB usage data after the license is issued. All billing and usage accounting happens locally via the **acaas** chart.
+
+### 4. Complete the Remaining Configuration
+
+Aside from enabling the offline toggle and providing the Cluster ID, all other sections are identical to a standard Self Hosted Production deployment (Global Administrative Settings, Release, Registry, Settings, Monitoring, Infra, TLS, Ingress & Gateway, NATS, and more). For the complete field-by-field walkthrough, follow the [Self Hosted Production](selfhosted-production.md) guide.
+
+### 5. Generate Installer and Documentation
+
+Click the "Deploy" button to submit your information. AppsCode will generate the installer and provide the necessary documentation.
+
+### 6. Deploy KubeDB Platform
+
+Follow the documentation provided by AppsCode to deploy the KubeDB Platform. The generated instructions for an offline deployment include an extra step to install the **acaas** chart, which carries the billing-related frontend and backend deployments. This chart is deployed *only* in offline mode.
+
+```bash
+curl -fsSLO https://appscode.ninja/links/installer/<id>/offline/<token>/archive.tar.gz
+tar -xzvf archive.tar.gz
+
+# Install FluxCD
+# Install ACE
+# It may take up to 10 mins to get everything into a running state
+
+# Install acaas
+helm upgrade -i acaas \
+  oci://ghcr.io/appscode-charts/acaas \
+  --version v2026.6.19 \
+  --namespace ace --create-namespace \
+  --values=./acaas-values.yaml \
+  --wait --debug --burst-limit=10000
+```
+
+<br/>
+
+![Acaas Chart](../../images/acaas-chart.png)
+
+> [!IMPORTANT]
+> The **acaas** chart contains the billing-related frontend and backend deployments. It is what keeps all usage and billing data inside your cluster, so it is installed in offline mode only — no other deployment type installs this chart.
+
+### 7. Explore the Deployed Platform
+
+Once deployed, access the **KubeDB Platform** using the configured IP or domain. Log in with the admin account credentials provided during the creation process.
+
+<br/>
+
+![Ace Dashboard](../../images/ace-dashboard.png)
+
+### 8. Importing Additional DBaaS Clusters
+
+When importing other DBaaS clusters into an offline platform, the platform cannot reach AppsCode to obtain a license automatically. The platform admin must acquire the license for each new cluster manually and supply it during import:
+
+1. Obtain the license for the new cluster from the [AppsCode portal](https://appscode.com) yourself.
+2. Provide that license in the license field while importing the cluster.
+
+> [!NOTE]
+> This manual step applies only to offline mode. In online deployments the license is fetched automatically during import.
+
+## Get Support
+
+If you encounter any challenges during the deployment or have questions, reach out to AppsCode support for assistance.