Pin view options button to leading toolbar edge on macOS

Place the view options control on the leading (`.navigation`) edge on
macOS so it is consistently the first/leftmost toolbar button across all
views, instead of sitting on the right next to the search field in
search views and on the left in non-search views.

Each affected view gains a computed `viewOptionsPlacement` (`.navigation`
on macOS, `.primaryAction` elsewhere) so iOS/iPadOS/tvOS keep the
button trailing. Search-style views (Search, InstanceBrowse) declare the
view options item first so it renders left of the search-filters button;
their flexible spacer is kept to right-pin the search field. Channel's
fixed spacer between view options and the channel menu is now iOS-only.

Yattee/Views/Instances/InstanceBrowseView.swift

@@ -122,6 +122,15 @@ struct InstanceBrowseView: View {
         )
     }
 
+    /// View options button lives on the leading edge on macOS, trailing elsewhere.
+    private var viewOptionsPlacement: ToolbarItemPlacement {
+        #if os(macOS)
+        .navigation
+        #else
+        .primaryAction
+        #endif
+    }
+
     var body: some View {
         let backgroundStyle: ListBackgroundStyle = listStyle == .inset ? .grouped : .plain
         GeometryReader { geometry in
@@ -332,6 +341,20 @@ struct InstanceBrowseView: View {
         .navigationTitle(instance.displayName)
         .toolbarTitleDisplayMode(.inlineLarge)
         .toolbar {
+            // View options first so it is the leftmost navigation item on macOS.
+            ToolbarItem(placement: viewOptionsPlacement) {
+                Button {
+                    showViewOptions = true
+                } label: {
+                    Label(String(localized: "viewOptions.title"), systemImage: "slider.horizontal.3")
+                }
+                .liquidGlassTransitionSource(id: "instanceBrowseViewOptions", in: sheetTransition)
+                #if os(macOS)
+                .popover(isPresented: $showViewOptions, arrowEdge: .bottom) {
+                    viewOptionsSheetContent
+                }
+                #endif
+            }
             #if os(macOS)
             if #available(macOS 26, *) {
                 // Search filters button appears only while showing search results.
@@ -372,25 +395,12 @@ struct InstanceBrowseView: View {
                         .fixedSize()
                 }
             }
-            // Pin the trailing group (search field + toolbar buttons) to the right edge,
+            // Pin the trailing group (search field) to the right edge,
             // matching the global Search view.
             if #available(macOS 26, *) {
                 ToolbarSpacer(.flexible, placement: .primaryAction)
             }
             #endif
-            ToolbarItem(placement: .primaryAction) {
-                Button {
-                    showViewOptions = true
-                } label: {
-                    Label(String(localized: "viewOptions.title"), systemImage: "slider.horizontal.3")
-                }
-                .liquidGlassTransitionSource(id: "instanceBrowseViewOptions", in: sheetTransition)
-                #if os(macOS)
-                .popover(isPresented: $showViewOptions, arrowEdge: .bottom) {
-                    viewOptionsSheetContent
-                }
-                #endif
-            }
         }
         #endif
         #if !os(macOS)