chore: Replace plain editor with advanced editor (#13071)

# Pull Request Template

## Description

This PR reverts the plain text editor back to the **advanced editor**,
which was previously removed in
[https://github.com/chatwoot/chatwoot/pull/13058](https://github.com/chatwoot/chatwoot/pull/13058).
All channels now use the **ProseMirror editor**, with formatting applied
based on each channel’s configuration.

This PR also fixes issues where **new lines were not properly preserved
during Markdown serialization**, for both:

* `Enter or CMD/Ctrl+enter` (new paragraph)
* `Shift+Enter` (`hard_break`)

Additionally, it resolves related **[Sentry
issue](https://chatwoot-p3.sentry.io/issues/?environment=production&project=4507182691975168&query=is%3Aunresolved%20markdown&referrer=issue-list&statsPeriod=7d)**.

With these changes:

* Line breaks and spacing are now preserved correctly when saving canned
responses.
* When editing a canned response, the content retains the exact spacing
and formatting as saved in editor.
* Canned responses are now correctly converted to plain text where
required and displayed consistently in the canned response list.

### https://github.com/chatwoot/prosemirror-schema/pull/38

---

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?



## Checklist:

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

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

package.json

@@ -33,7 +33,7 @@
   "dependencies": {
     "@breezystack/lamejs": "^1.2.7",
     "@chatwoot/ninja-keys": "1.2.3",
-    "@chatwoot/prosemirror-schema": "1.2.6",
+    "@chatwoot/prosemirror-schema": "1.3.4",
     "@chatwoot/utils": "^0.0.51",
     "@formkit/core": "^1.6.7",
     "@formkit/vue": "^1.6.7",