Add UX enhancements: carousel, filter chips, command palette, and more

- Replace featured section Stack with AdwCarousel + indicator dots
- Convert category grid to horizontal scrollable filter chips
- Add grid/list view toggle for catalog with compact row layout
- Add quick launch button on library list rows
- Add stale catalog banner when data is older than 7 days
- Add command palette (Ctrl+K) for quick app search and launch
- Show specific app names in update notifications
- Add per-app auto-update toggle (skip updates switch)
- Add keyboard shortcut hints to button tooltips
- Add source trust badges (AppImageHub/Community) on catalog tiles
- Add undo-based uninstall with toast and record restoration
- Add type-to-search in library view
- Use human-readable catalog source labels
- Show Launch button for installed apps in catalog detail
- Replace external browser link with inline AppImage explainer dialog

data/app.driftwood.Driftwood.gschema.xml

@@ -36,7 +36,7 @@
         <choice value='recently-added'/>
         <choice value='size'/>
       </choices>
-      <default>'name'</default>
+      <default>'recently-added'</default>
       <summary>Library sort mode</summary>
       <description>How to sort the library: name, recently-added, or size.</description>
     </key>