Improve Mobile UI for dialogs and action dropdowns (#16222)

Improve Mobile UI for dialogs and action dropdowns (#16222)

* fix: Always show conversation item actions

* feat: Improve Alert Dialog and Dialog mobile UI

* feat: Add settings reset to default confirmation

* fix: Close Edit dialog on save

* chore: update webui build output

* webui: implement proper z-index system and scroll management

- Add CSS variable for centralized z-index control
- Fix dropdown positioning with Settings dialog conflicts
- Prevent external scroll interference with proper event handling
- Clean up hardcoded z-index values for maintainable architecture

* webui: ensured the settings dialog enforces dynamic viewport height on mobile while retaining existing desktop sizing overrides

* feat: Use `dvh` instead of computed px height for dialogs max height on mobile

* chore: update webui build output

* feat: Improve Settings fields UI

* chore: update webui build output

* chore: update webui build output

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Co-authored-by: Pascal <redacted>