style(ui): refine picker presentation

ShadowsocksX-NG2/App/UI/Home/ModeCard.swift

@@ -27,7 +27,6 @@ struct ModeCard: View {
                   Text(action.label).tag(action)
                 }
               }
-              .pickerStyle(.segmented)
               .labelsHidden()
               .frame(maxWidth: .infinity, alignment: .leading)
             }

ShadowsocksX-NG2/App/UI/Rules/RulesPresetView.swift

@@ -4,14 +4,15 @@ struct RulesPresetView: View {
   @ObservedObject var workspaces: RulesWorkspaces
 
   var body: some View {
-    VStack(spacing: 0) {
+    VStack(alignment: .leading, spacing: 0) {
       Picker("规则预设", selection: $workspaces.selectedPreset) {
         ForEach(RulePreset.allCases, id: \.self) { preset in
           Text(preset.label).tag(preset)
         }
       }
       .pickerStyle(.segmented)
-      .padding()
+      .padding(.top)
+      .padding(.horizontal)
       RulesView(workflow: workspaces.current).id(workspaces.selectedPreset)
     }
   }