feat(cat-voices): handle markdown unknown embeds in VoicesRichText

[dt-iohk]

Description

• Handles markdown unknown embeds in VoicesRichText (divider).
• Adds on the fly recognition for the hr markdown element (---).

Note the following limitations:

• The flutter_quill has limited built-in support for recognizing formatting patterns on the fly. This means when the user will enter i.e. >> it will not immediately appear as a blockquote. The user must save it, open in edit again and only then this renders as a blockquote. The reason for this behavior is that the MarkdownCodec from the markdown_quill is only run when clicking the Edit button. flutter_quill has an API for recognizing formatting patterns but it's currently very limited and can only handle some limited cases (see: SpaceShortcutEvent).
• The toolbar header inside of the VoicesRichText editor has only handful of formatting styles but many many more are supported by flutter_quill and markdown_quill as listed in the Examples below.

Related Issue(s)

Part of #3746

Screenshots

Divider support:

Screen.Recording.2025-12-01.at.20.10.59.mov

All supported markdown styles and attributes:

Screen.Recording.2025-12-01.at.20.15.36.mov

Examples

# Heading 1
## Heading 2
### Heading 3
#### Heading 4
##### Heading 5
###### Heading 6

---

# Text Formatting

**Bold text**

__Bold text__

*Italic text*

_Italic text_

***Bold italic***

___Bold italic___

~~Strikethrough~~

`Inline code`

==Highlight (not supported)==

Line with a break  
Second line

[Link to external website](https://google.com)

---

# Blockquotes

> This is a quote.
>> This is a nested quote.

---

# Lists

## Unordered lists

- Item A
- Item B
  - Sub item B1
  - Sub item B2
* Another style
+ Another style

## Ordered lists

1. First item
2. Second item
3. Third item

Auto-numbering:
1. Item
1. Item
1. Item

---

# Task Lists (not supported)

- [ ] Not done
- [x] Done

---

# Code Blocks

## Fenced code block

```dart
void main() {
  print("Hello, world!");
}

Not supported:

• tables
• checkboxes [ ]
• highlights == some text ==

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

📚 Docs Preview

The docs for this PR can be previewed at the following URL:

https://docs.dev.projectcatalyst.io/voices/fix/voices-rich-text-markdown-fixes-3746