chore: Improvements in pending FAQs (#12755)

# Pull Request Template

## Description

**This PR includes:**

1. Added URL-based filter persistence for the responses pages, including
page and search parameters.
2. Introduced a new empty state variant for pending FAQs — without a
backdrop and with a “Clear Filters” option.
3. Made the actions, filter, and search row remain fixed at the top
while scrolling.

Fixes
https://linear.app/chatwoot/issue/CW-5852/improvements-in-pending-faqs

## Type of change

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

## How Has This Been Tested?

### Loom video
https://www.loom.com/share/1d9eee68c0684f0ab05e08b4ca1e0ce9


## 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-next/captain/PageLayout.vue

@@ -114,6 +114,7 @@ const handlePageChange = event => {
             <slot name="action" />
           </div>
         </div>
+        <slot name="subHeader" />
       </div>
     </header>
     <main class="flex-1 px-6 overflow-y-auto">