Pin search bar to right of macOS toolbar in list views

Match the global Search view by pinning the searchable field and
trailing buttons to the right edge on macOS 26 via a flexible
ToolbarSpacer at .primaryAction. Applied to History, Bookmarks,
Manage Channels, Downloads, Instance Browse, and PeerTube Explore.

In History, the clear-history item moves from .automatic to
.primaryAction so it groups with the other trailing controls.

Yattee/Views/Instances/InstanceBrowseView.swift

@@ -340,6 +340,13 @@ struct InstanceBrowseView: View {
         .navigationTitle(instance.displayName)
         .toolbarTitleDisplayMode(.inlineLarge)
         .toolbar {
+            #if os(macOS)
+            // Pin the trailing group (search field + toolbar buttons) to the right edge,
+            // matching the global Search view.
+            if #available(macOS 26, *) {
+                ToolbarSpacer(.flexible, placement: .primaryAction)
+            }
+            #endif
             ToolbarItem(placement: .primaryAction) {
                 Button {
                     showViewOptions = true