Add full content to Markdown-Node

### Current Behavior

Content shows as text

### Expected Behavior

Content shows as markdown

### Steps To Reproduce

1. make a Markdown-Text in a Template-Node
2. connect to Dashboard Markdown-Node
3. add {{ msg.payload }} to the Markdown-Node

Example:
```
[
{
"id": "fe10b74873aebcc0",
"type": "tab",
"label": "Flow 5",
"disabled": false,
"info": "",
"env": []
},
{
"id": "66d1e5776bc7e3ed",
"type": "inject",
"z": "fe10b74873aebcc0",
"name": "",
"props": [
{
"p": "payload"
}
],
"repeat": "",
"crontab": "",
"once": false,
"onceDelay": 0.1,
"topic": "",
"payload": "",
"payloadType": "str",
"x": 90,
"y": 100,
"wires": [
[
"25c4ceaa8ff3c491"
]
]
},
{
"id": "25c4ceaa8ff3c491",
"type": "template",
"z": "fe10b74873aebcc0",
"name": "",
"field": "payload",
"fieldType": "msg",
"format": "markdown",
"syntax": "plain",
"template": "# Markdown Content\n\n## Secondary Header\n\n### Third Header\n\nParagraph here...\n\ninline `` with other text either side\n\n```js\n// multiline\nfunction () {\n console.log('hello world')\n}\n```\n\n- List Item 1\n- List Item 1\n- List Item 1\n- List Item 1\n\n[Hyperlink](https://news.bbc.co.uk)\n\n---\n\n> Lorum Ipsum Quotation Over two lines \n\n| Header 1 | Header 2 |\n|-|-|\n| eins | zwei |",
"output": "str",
"x": 300,
"y": 100,
"wires": [
[
"c61f4317ad20f535"
]
]
},
{
"id": "c61f4317ad20f535",
"type": "ui-markdown",
"z": "fe10b74873aebcc0",
"group": "be8440d16f7098fc",
"name": "",
"order": 2,
"width": 0,
"height": 0,
"content": "{{ msg.payload }}",
"className": "",
"x": 490,
"y": 100,
"wires": [
[]
]
},
{
"id": "be8440d16f7098fc",
"type": "ui-group",
"name": "Group Name",
"page": "60fb1b70653660dd",
"width": "6",
"height": "1",
"order": 1,
"showTitle": true,
"className": "",
"visible": "true",
"disabled": "false"
},
{
"id": "60fb1b70653660dd",
"type": "ui-page",
"name": "Obsidian",
"ui": "863357a5c2346037",
"path": "/page3",
"icon": "home",
"layout": "grid",
"theme": "07f2253c8612a459",
"order": 4,
"className": "",
"visible": "true",
"disabled": "false"
},
{
"id": "863357a5c2346037",
"type": "ui-base",
"name": "My Dashboard",
"path": "/dashboard",
"includeClientData": true,
"acceptsClientConfig": [
"ui-notification",
"ui-control"
],
"showPathInSidebar": false,
"showPageTitle": true,
"navigationStyle": "default",
"titleBarStyle": "default"
},
{
"id": "07f2253c8612a459",
"type": "ui-theme",
"name": "Default Theme",
"colors": {
"surface": "#ffffff",
"primary": "#0094CE",
"bgPage": "#eeeeee",
"groupBg": "#ffffff",
"groupOutline": "#cccccc"
},
"sizes": {
"pagePadding": "12px",
"groupGap": "12px",
"groupBorderRadius": "4px",
"widgetGap": "12px"
}
}
]
```

### Environment

- Dashboard version: 1.13.0
- Node-RED version: 4.0.2
- Node.js version: 18.20.3
- npm version: 10.7.0
- Platform/OS: Debian 12.6 (64-bit)
- Browser: Chromium 126.0.6478.126

### Have you provided an initial effort estimate for this issue?

I am not a FlowFuse team member

Start by reproducing the provided flow with a Template-Node feeding the Dashboard Markdown-Node, then trace the Markdown-Node rendering path. Done means content supplied through {{ msg.payload }} is rendered as markdown, including headings, code, lists, links, quotations, and tables, rather than displayed as plain text.

Written by the indexing model from the issue text.