chore: add docs/update-server.md from MokoStandards

docs/update-server.md

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+<!--
+Copyright (C) 2026 Moko Consulting <hello@mokoconsulting.tech>
+
+This file is part of a Moko Consulting project.
+
+SPDX-License-Identifier: GPL-3.0-or-later
+
+# FILE INFORMATION
+DEFGROUP: MokoCassiopeia.Documentation
+INGROUP: MokoStandards.Templates
+REPO: https://github.com/mokoconsulting-tech/MokoCassiopeia
+PATH: /docs/update-server.md
+VERSION: 04.04.00
+BRIEF: How this extension's Joomla update server file (update.xml) is managed
+-->
+
+# Joomla Update Server
+
+[![MokoStandards](https://img.shields.io/badge/MokoStandards-04.04.00-blue)](https://github.com/mokoconsulting-tech/MokoStandards)
+
+This document explains how `update.xml` is automatically managed for this Joomla extension following the [Joomla Update Server specification](https://docs.joomla.org/Deploying_an_Update_Server).
+
+## How It Works
+
+Joomla checks for extension updates by fetching an XML file from the URL defined in the `<updateservers>` tag in the extension's XML manifest. MokoStandards generates this file automatically.
+
+### Automatic Generation
+
+| Event | Workflow | `<tag>` | `<version>` |
+|-------|----------|---------|-------------|
+| Merge to `main` | `auto-release.yml` | `stable` | `XX.YY.ZZ` |
+| Push to `dev/**` | `deploy-dev.yml` | `development` | `development` |
+| Push to `rc/**` | `deploy-dev.yml` | `rc` | `XX.YY.ZZ-rc` |
+
+### Generated XML Structure
+
+```xml
+<?xml version="1.0" encoding="utf-8"?>
+<updates>
+    <update>
+        <name>Extension Name</name>
+        <description>Extension Name update</description>
+        <element>com_extensionname</element>
+        <type>component</type>
+        <version>01.02.03</version>
+        <client>site</client>
+        <folder>system</folder>          <!-- plugins only -->
+        <tags>
+            <tag>stable</tag>
+        </tags>
+        <infourl title="Extension Name">https://github.com/.../releases/tag/v01.02.03</infourl>
+        <downloads>
+            <downloadurl type="full" format="zip">https://github.com/.../releases/download/v01.02.03/com_ext-01.02.03.zip</downloadurl>
+        </downloads>
+        <targetplatform name="joomla" version="((5\.[0-9])|(6\.[0-9]))" />
+        <php_minimum>8.2</php_minimum>   <!-- if present in manifest -->
+        <maintainer>Moko Consulting</maintainer>
+        <maintainerurl>https://mokoconsulting.tech</maintainerurl>
+    </update>
+</updates>
+```
+
+### Metadata Source
+
+All metadata is extracted from the extension's XML manifest (`src/*.xml`) at build time:
+
+| XML Element | Source | Notes |
+|-------------|--------|-------|
+| `<name>` | `<name>` in manifest | Extension display name |
+| `<element>` | `<element>` in manifest | Must match installed extension identifier |
+| `<type>` | `type` attribute on `<extension>` | `component`, `module`, `plugin`, `library`, `package`, `template` |
+| `<client>` | `client` attribute on `<extension>` | `site` or `administrator` — **required for plugins and modules** |
+| `<folder>` | `group` attribute on `<extension>` | Plugin group (e.g., `system`, `content`) — **required for plugins** |
+| `<targetplatform>` | `<targetplatform>` in manifest | Falls back to Joomla 5.x / 6.x if not specified |
+| `<php_minimum>` | `<php_minimum>` in manifest | Included only if present |
+
+### Extension Manifest Setup
+
+Your XML manifest must include an `<updateservers>` tag pointing to the `update.xml` on the `main` branch:
+
+```xml
+<extension type="component" client="site" method="upgrade">
+    <name>My Extension</name>
+    <element>com_myextension</element>
+    <!-- ... -->
+    <updateservers>
+        <server type="extension" name="My Extension Updates">
+            https://raw.githubusercontent.com/mokoconsulting-tech/MokoCassiopeia/main/update.xml
+        </server>
+    </updateservers>
+</extension>
+```
+
+### Branch Lifecycle
+
+```
+dev/XX.YY.ZZ  →  rc/XX.YY.ZZ  →  main  →  version/XX.YY
+(development)     (rc)              (stable)    (frozen snapshot)
+```
+
+1. **Development** (`dev/**`): `update.xml` with `<tag>development</tag>`, download points to branch archive
+2. **Release Candidate** (`rc/**`): `update.xml` with `<tag>rc</tag>`, version set to `XX.YY.ZZ-rc`
+3. **Stable Release** (merge to `main`): `update.xml` with `<tag>stable</tag>`, download points to GitHub Release asset
+4. **Frozen Snapshot** (`version/XX.YY`): immutable, never force-pushed
+
+### Health Checks
+
+The `repo_health.yml` workflow verifies on every commit:
+
+- `update.xml` exists in the repository root
+- XML manifest exists with `<extension>` tag
+- `<version>`, `<name>`, `<author>`, `<namespace>` tags present
+- Extension `type` attribute is valid
+- Language `.ini` files exist
+- `index.html` directory listing protection in `src/`, `src/admin/`, `src/site/`
+
+---
+
+*Managed by [MokoStandards](https://github.com/mokoconsulting-tech/MokoStandards). See [docs/workflows/update-server.md](https://github.com/mokoconsulting-tech/MokoStandards/blob/main/docs/workflows/update-server.md) for the full specification.*