fix: oversized email signature images in Letter render (#14144)

# Pull Request Template

## Description

This PR fixes an issue where signature images (with
`?cw_image_height=...`) render at their original large size in the email
bubble.

### Cause

Renderer output:

```html
<img src="..." height="24px" width="auto" />
```

Email UI and clients (Gmail, Outlook) apply CSS like:
`img { max-width: 100%; height: auto; }`
This overrides `height="24px"`.
Other channels work because they use inline styles (`style="height:
24px;"`).


### Solution

Use inline style instead:

```html
<img src="..." style="height: 24px;" />
```


### Why backend fix

* Fixes root cause and aligns Ruby + JS renderers
* Works in both Chatwoot UI and recipient inboxes
* Covers all email-rendered content
* Minimal change


Fixes
https://linear.app/chatwoot/issue/CW-6948/email-signature-image-renders-oversized-in-chatwoot-ui

## Type of change

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

## How Has This Been Tested?

#### Screenshots

**Before**
<img width="1637" height="377" alt="image"
src="https://github.com/user-attachments/assets/0477f6fb-3b95-4fc3-9ea8-f59b71e27f47"
/>


**After**
<img width="1637" height="289" alt="image"
src="https://github.com/user-attachments/assets/de5ea4c1-8452-4c5f-aeb1-e1e11e0fe7d5"
/>



## 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

lib/base_markdown_renderer.rb

@@ -29,11 +29,15 @@ class BaseMarkdownRenderer < CommonMarker::HtmlRenderer
 
   def render_img_tag(src, title, height = nil)
     title_attribute = title.present? ? " title=\"#{title}\"" : ''
-    height_attribute = height ? " height=\"#{height}\" width=\"auto\"" : ''
+    # Use inline style instead of the HTML height attribute: email clients and
+    # the in-app Letter view both run images through CSS (e.g. prose /
+    # lettersanitizer's `img { height: auto }`) which overrides presentational
+    # attributes. Inline style has higher specificity and survives.
+    style_attribute = height ? " style=\"height: #{height};\"" : ''
 
     plain do
       # plain ensures that the content is not wrapped in a paragraph tag
-      out("<img src=\"#{src}\"#{title_attribute}#{height_attribute} />")
+      out("<img src=\"#{src}\"#{title_attribute}#{style_attribute} />")
     end
   end
 end

spec/lib/base_markdown_renderer_spec.rb

@@ -12,7 +12,7 @@ describe BaseMarkdownRenderer do
     context 'when image has a height' do
       it 'renders the img tag with the correct attributes' do
         markdown = '![Sample Title](https://example.com/image.jpg?cw_image_height=100)'
-        expect(render_markdown(markdown)).to include('<img src="https://example.com/image.jpg?cw_image_height=100" height="100" width="auto" />')
+        expect(render_markdown(markdown)).to include('<img src="https://example.com/image.jpg?cw_image_height=100" style="height: 100;" />')
       end
     end