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>

app/javascript/dashboard/routes/dashboard/settings/canned/Index.vue

@@ -6,6 +6,7 @@ import BaseSettingsHeader from '../components/BaseSettingsHeader.vue';
 import { computed, onMounted, ref, defineOptions } from 'vue';
 import { useI18n } from 'vue-i18n';
 import { useStoreGetters, useStore } from 'dashboard/composables/store';
+import { useMessageFormatter } from 'shared/composables/useMessageFormatter';
 
 import Button from 'dashboard/components-next/button/Button.vue';
 
@@ -17,6 +18,8 @@ const getters = useStoreGetters();
 const store = useStore();
 const { t } = useI18n();
 
+const { getPlainText } = useMessageFormatter();
+
 const showAddPopup = ref(false);
 const loading = ref({});
 const showEditPopup = ref(false);
@@ -182,7 +185,7 @@ const tableHeaders = computed(() => {
               {{ cannedItem.short_code }}
             </td>
             <td class="py-4 ltr:pr-4 rtl:pl-4 md:break-all whitespace-normal">
-              {{ cannedItem.content }}
+              {{ getPlainText(cannedItem.content) }}
             </td>
             <td class="py-4 flex justify-end gap-1">
               <Button