fix: Block inline images in message signatures (#13772)

# Pull Request Template

## Description

This PR includes, block inline images in message signatures and prevent
auto signature insertion when editor is disabled.

- Strip inline base64 images from signature on save and show warning
message
- Add `INLINE_IMAGE_WARNING` translation key for signature inline image
removal notification
- Add disabled check to `addSignature()` to prevent signature insertion
when editor is disabled
- Add `isEditorDisabled` checks to signature toggle logic in
`toggleSignatureForDraft()`, `replaceText()`, and `clearMessage()`
- Remove unused `replaceText` from the codebase, which belongs to old
`textarea` editor

Fixes
https://linear.app/chatwoot/issue/CW-6588/the-browser-hangs-when-the-message-signature-contains-inline-image

## Type of change

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

## How Has This Been Tested?

### Loom video
https://www.loom.com/share/fb556b46a12a4308a737eed732d5ed73


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [ ] 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
- [ ] 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/helper/specs/editorHelper.spec.js

@@ -15,6 +15,7 @@ import {
   getMenuAnchor,
   calculateMenuPosition,
   stripUnsupportedFormatting,
+  stripInlineBase64Images,
 } from '../editorHelper';
 import { FORMATTING } from 'dashboard/constants/editor';
 import { EditorState } from '@chatwoot/prosemirror-schema';
@@ -423,6 +424,36 @@ describe('extractTextFromMarkdown', () => {
   });
 });
 
+describe('stripInlineBase64Images', () => {
+  it('removes markdown data:image base64 images and sets hasInlineImages', () => {
+    const content =
+      'Hello\n![x](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAE)\nWorld';
+    const { sanitizedContent, hasInlineImages } =
+      stripInlineBase64Images(content);
+
+    expect(hasInlineImages).toBe(true);
+    expect(sanitizedContent).not.toContain('data:image/png;base64');
+    expect(sanitizedContent).toContain('Hello');
+    expect(sanitizedContent).toContain('World');
+  });
+
+  it('leaves hosted image markdown unchanged', () => {
+    const content = '![](https://example.com/logo.png)';
+    const { sanitizedContent, hasInlineImages } =
+      stripInlineBase64Images(content);
+
+    expect(hasInlineImages).toBe(false);
+    expect(sanitizedContent).toBe(content);
+  });
+
+  it('returns empty hasInlineImages for empty input', () => {
+    expect(stripInlineBase64Images('')).toEqual({
+      sanitizedContent: '',
+      hasInlineImages: false,
+    });
+  });
+});
+
 describe('insertAtCursor', () => {
   it('should return undefined if editorView is not provided', () => {
     const result = insertAtCursor(undefined, schema.text('Hello'), 0);