Fix collapsed AddSource/EditSource sheets on macOS

Add macOS-only minimum frame to NavigationStack so the sheet has
intrinsic size. Matches the pattern already used in
PeerTubeInstancesExploreView.

Yattee/Assets.xcassets/Yattee2.brandassets/Top Shelf Image Wide.imageset/Contents.json

@@ -4,6 +4,10 @@
       "filename" : "TopShelf-Wide.png",
       "idiom" : "tv",
       "scale" : "1x"
+    },
+    {
+      "idiom" : "tv",
+      "scale" : "2x"
     }
   ],
   "info" : {

Yattee/Assets.xcassets/Yattee2.brandassets/Top Shelf Image.imageset/Contents.json

@@ -4,6 +4,10 @@
       "filename" : "TopShelf.png",
       "idiom" : "tv",
       "scale" : "1x"
+    },
+    {
+      "idiom" : "tv",
+      "scale" : "2x"
     }
   ],
   "info" : {

Yattee/Views/Settings/AddSourceView.swift

@@ -88,6 +88,9 @@ struct AddSourceView: View {
                     )
                 }
         }
+        #if os(macOS)
+        .frame(minWidth: 500, minHeight: 450)
+        #endif
         .sheet(isPresented: $showingNetworkDiscovery) {
             NetworkShareDiscoverySheet(filterType: selectedShareType) { share in
                 handleSelectedShare(share)

Yattee/Views/Settings/EditSourceView.swift

@@ -101,6 +101,9 @@ private struct EditRemoteServerContent: View {
                 }
                 .accessibilityIdentifier("editSource.view")
         }
+        #if os(macOS)
+        .frame(minWidth: 500, minHeight: 450)
+        #endif
         #endif
     }