fix: markdown alert syntax support with unsafe_allow_html = true

[hexart]

Issue

When unsafe_allow_html = true, markdown-alert component has two issues:

1. The ::: syntax fails to parse correctly
2. HTML alert tag is not supported at all

Solution

1. Fixed alert syntax parsing when unsafe_allow_html = true
2. Added HTML tag support for alerts

Verified

1. With unsafe_allow_html = true:

   • Verify both ::: syntax and HTML tag syntax work
   • Check all alert types render correctly
   • Confirm styling and icons are consistent across both syntaxes

2. With unsafe_allow_html = false:

   • Verify ::: syntax works as before
   • Confirm HTML tags are escaped and shown as text

Usage

await cl.Message(content="::: idea\nInnovative idea\n:::\n\n").send()

<alert type="idea">Innovative idea</alert>

Addition

Add type validation in both markdown mode and html tag mode.
If type error, alert will fall back to info type.

Testing code

Details

import chainlit as cl

MARKDOWN_DEMO = '''
# Markdown & Alert Demo

## Text Formatting
**Bold text** and *italic text*
~~Strikethrough~~ and `inline code`

## Lists
### Unordered List
- First item
- Second item
 - Nested item
 - Another nested item

### Ordered List
1. First step
2. Second step
  1. Sub-step one
  2. Sub-step two

## Table
| Header 1 | Header 2 |
|----------|----------|
| Cell 1   | Cell 2   |
| Cell 3   | Cell 4   |

## Quote
> This is the quote text.
## Alerts
#### Basic alerts
::: InFo
Information message with a list:
Item 1
Item 2
:::

::: note
Note message
:::

::: tip
Helpful tip with code
:::

::: Important
Critical information!
:::

::: warning
Warning with emphasis
:::

::: caution
Caution message
:::
#### Development related
::: debug
Debug information
:::

::: example
Example usage
:::
#### Functional alerts
::: success
Operation successful
:::

::: help
Help message
:::

::: idea
Innovative idea
:::
#### Status alerts
::: pending
Work in progress
:::

::: security
Security notice
:::

::: beta
Beta feature
:::

::: best-practice
Recommended practice
:::

::: unknown
Unknown type, falling back to info type
:::

## HTML Test
<div style="color: blue;">
  <h3>HTML Content</h3>
  <ul>
    <li>HTML list item 1</li>
    <li>HTML list item 2</li>
  </ul>
</div>

<table border="1">
  <tr>
    <th>HTML Table</th>
    <th>Header 2</th>
  </tr>
  <tr>
    <td>Data 1</td>
    <td>Data 2</td>
  </tr>
</table>
<h3>Basic alerts</h3>
<alert type="Info">Information message</alert>
<alert type="noTe">Note message</alert>
<alert type="TIP">Helpful tip with code</alert>
<alert type="important">Critical information!</alert>
<alert type="warning">Warning with emphasis</alert>
<alert type="caution">Caution message</alert>
<h3>Development related</h3>
<alert type="debug">Debug information</alert>
<alert type="example">Example usage</alert>
<h3>Functional alerts</h3>
<alert type="success">Operation successful</alert>
<alert type="help">Help message</alert>
<alert type="idea">Innovative idea</alert>
<h3>Status alerts</h3>
<alert type="pending">Work in progress</alert>
<alert type="security">Security notice</alert>
<alert type="beta">Beta feature</alert>
<alert type="Best-practice">Recommended practice</alert>
<alert type="unknown">Unknown type, falling back to info type</alert>

## LaTeX Test
Inline math: $E = mc^2$
'''

@cl.on_chat_start
async def send_demo():
    await cl.Message(content=MARKDOWN_DEMO).send()

CAUTION:
This demo will cause a bug of nested scrolling pages with latex = true.

[willydouhard]

lgtm