fix: Usability issues in conversation card context menu (#10971)

# Pull Request Template

## Description

The PR includes usability feedback fixes for the conversation card
context menu. A "Mark as Read" option has been added after "Mark as
Unread" to prevent misclicks due to shifting menu positions.
Additionally, a separator line has been introduced for better grouping
and clarity

#### **Orders**  
<img width="210" alt="image"
src="https://github.com/user-attachments/assets/d7c04356-7cfb-4f43-ac55-beb4167f91e9"
/>
<img width="210" alt="image"
src="https://github.com/user-attachments/assets/593acd58-39cf-4b25-b119-03b89cb3528c"
/>

**Fixes** https://linear.app/chatwoot/issue/CW-4088/usability-feedback

## Type of change

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

## How Has This Been Tested?

### **Loom video**

https://www.loom.com/share/59f8ad3bf4054b299bfcffc0ba24eca1?sid=98fbb67d-c3e9-4fa4-9b04-2a7cb3bf8568

## 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

app/javascript/dashboard/i18n/locale/en/conversation.json

@@ -117,6 +117,7 @@
       "PENDING": "Mark as pending",
       "RESOLVED": "Mark as resolved",
       "MARK_AS_UNREAD": "Mark as unread",
+      "MARK_AS_READ": "Mark as read",
       "REOPEN": "Reopen conversation",
       "SNOOZE": {
         "TITLE": "Snooze",