Fix collapsed sheets on macOS across the app

Add macOS-only minimum frame sizing to sheets that wrap a
NavigationStack/Form without intrinsic size, so they render properly
instead of collapsing to just the toolbar. Affects Customize Home,
subscription/channel view options, playlist create/edit, search
filters, media browser options, instance picker, log filters, preset
editor, and legacy data import result.

Yattee/Views/Subscriptions/ManageChannelsView.swift

@@ -189,6 +189,9 @@ struct ManageChannelsView: View {
                 #endif
                 #endif
             }
+            #if os(macOS)
+            .frame(minWidth: 500, minHeight: 400)
+            #endif
             .presentationDetents([.height(360), .large])
             .presentationDragIndicator(.visible)
             .liquidGlassSheetContent(sourceID: "manageChannelsViewOptions", in: sheetTransition)

Yattee/Views/Subscriptions/SubscriptionsView.swift

@@ -341,6 +341,9 @@ struct SubscriptionsView: View {
                             #endif
                             #endif
                         }
+                        #if os(macOS)
+                        .frame(minWidth: 500, minHeight: 450)
+                        #endif
                         .presentationDetents([.height(420), .large])
                         .presentationDragIndicator(.visible)
                         .liquidGlassSheetContent(sourceID: "subscriptionsViewOptions", in: sheetTransition)