fix(themes): join Pafat's queries dropdown to its sibling at narrow widths (#8733)
In Pafat at narrow widths, the User queries dropdown inside `#nav_menu_actions.group` is visually disconnected from its sibling buttons: its right edge looks rounded but with a gap to its left neighbor (the search dropdown), so it doesn't visually cap the group cleanly. The cause is Pafat's existing rule
```css
.stick .btn + .dropdown > .btn,
.group .btn + .dropdown > .btn,
.group .dropdown + .dropdown > .btn {
border-left: none;
border-radius: 0 3px 3px 0;
}
```
which right-rounds **every** group dropdown that follows a button or another dropdown, not only the trailing one. When two group dropdowns sit side by side (the search dropdown followed by the queries dropdown), both end up right-rounded and look disconnected.
The fix adds `:last-child` to the two `.group` selectors so the right-radius only applies when the dropdown is the trailing element. Non-trailing group dropdowns then fall through to the base `.group .btn { border-radius: 0 }` rule and render with square corners, joining cleanly. A lone group dropdown (where `.dropdown` is `:only-child` of `.group`) is untouched, because it has no preceding sibling for the `+` combinator to match.
### Screenshots
#### Before, narrow Pafat: queries' right edge disconnected from search
<img width="316" height="179" alt="pafat before" src="https://github.com/user-attachments/assets/f5a5558f-e036-4cb6-8a6c-b33534de0ee1" />
#### After, narrow Pafat: queries joined to search and right-rounded as group cap
<img width="304" height="176" alt="pafat after" src="https://github.com/user-attachments/assets/65c371a0-f578-4a45-b797-5c669c8b293a" />
### Notes
- `.rtl.css` regenerated via `make rtl`.
- `npm run stylelint` passes.
- Verified at narrow width on FreshRSS 1.28.2-dev.
Co-authored-by: Bjørn A. Andersen <polybjorn@users.noreply.github.com>
polybjorn