feat: Standardize rich editor across all channels (#12600)

# Pull Request Template

## Description

This PR includes,

1. **Channel-specific formatting and menu options** for the rich reply
editor.
2. **Removal of the plain reply editor** and full **standardization** on
the rich reply editor across all channels.
3. **Fix for multiple canned responses insertion:**
* **Before:** The plain editor only allowed inserting canned responses
at the beginning of a message, making it impossible to combine multiple
canned responses in a single reply. This caused inconsistent behavior
across the app.
* **Solution:** Replaced the plain reply editor with the rich
(ProseMirror) editor to ensure a unified experience. Agents can now
insert multiple canned responses at any cursor position.
4. **Floating editor menu** for the reply box to improve accessibility
and overall user experience.
5. **New Strikethrough formatting option** added to the editor menu.

---

**Editor repo PR**:
https://github.com/chatwoot/prosemirror-schema/pull/36

Fixes https://github.com/chatwoot/chatwoot/issues/12517,
[CW-5924](https://linear.app/chatwoot/issue/CW-5924/standardize-the-editor),
[CW-5679](https://linear.app/chatwoot/issue/CW-5679/allow-inserting-multiple-canned-responses-in-a-single-message)

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

### Screenshot
**Dark**
<img width="850" height="345" alt="image"
src="https://github.com/user-attachments/assets/47748e6c-380f-44a3-9e3b-c27e0c830bd0"
/>

**Light**
<img width="850" height="345" alt="image"
src="https://github.com/user-attachments/assets/6746cf32-bf63-4280-a5bd-bbd42c3cbe84"
/>


## 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>
Co-authored-by: Pranav <pranav@chatwoot.com>
Co-authored-by: Vinay Keerthi <11478411+stonecharioteer@users.noreply.github.com>

app/models/channel/telegram.rb

@@ -130,30 +130,39 @@ class Channel::Telegram < ApplicationRecord
   def convert_markdown_to_telegram_html(text)
     # ref: https://core.telegram.org/bots/api#html-style
 
-    # escape html tags in text. We are subbing \n to <br> since commonmark will strip exta '\n'
-    text = CGI.escapeHTML(text.gsub("\n", '<br>'))
+    # Escape HTML entities first to prevent HTML injection
+    # This ensures only markdown syntax is converted, not raw HTML
+    escaped_text = CGI.escapeHTML(text)
 
-    # convert markdown to html
-    html = CommonMarker.render_html(text).strip
+    # Parse markdown with extensions:
+    # - strikethrough: support ~~text~~
+    # - hardbreaks: preserve all newlines as <br>
+    html = CommonMarker.render_html(escaped_text, [:HARDBREAKS], [:strikethrough]).strip
 
-    # remove all html tags except b, strong, i, em, u, ins, s, strike, del, a, code, pre, blockquote
-    stripped_html = Rails::HTML5::SafeListSanitizer.new.sanitize(html, tags: %w[b strong i em u ins s strike del a code pre blockquote],
-                                                                       attributes: %w[href])
+    # Convert paragraph breaks to double newlines to preserve them
+    # CommonMarker creates <p> tags for paragraph breaks, but Telegram doesn't support <p>
+    html_with_breaks = html.gsub(%r{</p>\s*<p>}, "\n\n")
 
-    # converted escaped br tags to \n
-    stripped_html.gsub('&lt;br&gt;', "\n")
+    # Remove opening and closing <p> tags
+    html_with_breaks = html_with_breaks.gsub(%r{</?p>}, '')
+
+    # Sanitize to only allowed tags
+    stripped_html = Rails::HTML5::SafeListSanitizer.new.sanitize(html_with_breaks, tags: %w[b strong i em u ins s strike del a code pre blockquote],
+                                                                                   attributes: %w[href])
+
+    # Convert <br /> tags to newlines for Telegram
+    stripped_html.gsub(%r{<br\s*/?>}, "\n")
   end
 
   def message_request(chat_id, text, reply_markup = nil, reply_to_message_id = nil, business_connection_id: nil)
-    text_payload = convert_markdown_to_telegram_html(text)
-
+    # text is already converted to HTML by MessageContentPresenter
     business_body = {}
     business_body[:business_connection_id] = business_connection_id if business_connection_id
 
     HTTParty.post("#{telegram_api_url}/sendMessage",
                   body: {
                     chat_id: chat_id,
-                    text: text_payload,
+                    text: text,
                     reply_markup: reply_markup,
                     parse_mode: 'HTML',
                     reply_to_message_id: reply_to_message_id