fix: Fix overlap issue with filter dropdown (#12133)

# Pull Request Template

## Description

This PR increase z-index of filter dropdown to prevent overlap with
other elements.

Fixes
https://linear.app/chatwoot/issue/CW-5394/update-z-index-for-filters

## Type of change

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

## How Has This Been Tested?

### Screenshot

<img width="823" height="250" alt="image"
src="https://github.com/user-attachments/assets/5788fc6d-a901-4d6a-8e8b-d4f49cccb12e"
/>



## 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/components/ChatListHeader.vue

@@ -98,7 +98,7 @@ const toggleConversationLayout = () => {
           />
           <div
             id="saveFilterTeleportTarget"
-            class="absolute z-40 mt-2"
+            class="absolute z-50 mt-2"
             :class="{ 'ltr:right-0 rtl:left-0': isOnExpandedLayout }"
           />
         </div>
@@ -124,7 +124,7 @@ const toggleConversationLayout = () => {
           />
           <div
             id="conversationFilterTeleportTarget"
-            class="absolute z-40 mt-2"
+            class="absolute z-50 mt-2"
             :class="{ 'ltr:right-0 rtl:left-0': isOnExpandedLayout }"
           />
         </div>
@@ -150,7 +150,7 @@ const toggleConversationLayout = () => {
         />
         <div
           id="conversationFilterTeleportTarget"
-          class="absolute z-40 mt-2"
+          class="absolute z-50 mt-2"
           :class="{ 'ltr:right-0 rtl:left-0': isOnExpandedLayout }"
         />
       </div>