Updates to use dynamic/responsive styles on web (#1351)

* Move most responsive queries to the hook

* Fix invalid CSS value

* Fixes to tablet render of post thread

* Fix overflow issues on web

* Fix search header on tablet

* Fix QP margin in web composer

* Fix: only apply double gutter once to flatlist (close #1368)

* Fix styles on discover feeds header

* Fix double discover links in multifeed

src/state/models/feeds/multi-feed.ts

@@ -111,7 +111,8 @@ export class PostsMultiFeedModel {
         uri: makeProfileLink(feedInfo.data.creator, 'feed', urip.rkey),
       })
     }
-    if (!this.hasMore) {
+    if (!this.hasMore && this.hasContent) {
+      // only show if hasContent to avoid double discover-feed links
       items.push({_reactKey: '__footer__', type: 'footer'})
     }
     return items