feat: Implement scroll-to-top for native TabView (#54)

* feat: implement scroll-to-top for native TabView using Combine

Implement proper SwiftUI approach for detecting tab reselection:
- Add Combine PassthroughSubject to capture all tab taps
- Create intermediate binding that publishes tap events
- Use onReceive to dispatch TabbarClickAction for scroll-to-top
- Works for both tab switches and same-tab taps
- Pure SwiftUI solution without UIKit introspection

This enables the native iOS behavior where tapping an active tab
scrolls content to the top, matching standard iOS app behavior.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* fix: update tab selection unconditionally for consistency

Apply Copilot suggestion to always update selectedTab binding value,
even when tapping the same tab. This ensures the TabView selection
stays in sync and simplifies the binding logic.

Setting the same value is harmless in SwiftUI and prevents potential
sync issues between the intermediate binding and the actual state.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Claude <[email protected]>

Author: graycreate

V2er/View/MainPage.swift

@@ -7,9 +7,11 @@
 //
 
 import SwiftUI
+import Combine
 
 struct MainPage: StateView {
     @EnvironmentObject private var store: Store
+    @State private var tabReselectionPublisher = PassthroughSubject<TabId, Never>()
 
     var bindingState: Binding<GlobalState> {
         $store.appState.globalState
@@ -22,10 +24,26 @@ struct MainPage: StateView {
         store.appState.feedState.feedInfo.unReadNums
     }
 
+    // Create an intermediate binding that captures all tab selections
+    // This is the proper SwiftUI way to detect same-tab taps without UIKit
+    private var tabSelection: Binding<TabId> {
+        Binding(
+            get: { selectedTab.wrappedValue },
+            set: { newValue in
+                // Publish the tap event before changing the value
+                // This allows us to detect same-tab taps
+                tabReselectionPublisher.send(newValue)
+
+                // Always update the selection to maintain consistency
+                selectedTab.wrappedValue = newValue
+            }
+        )
+    }
+
     var body: some View {
         NavigationView {
             ZStack {
-                TabView(selection: selectedTab) {
+                TabView(selection: tabSelection) {
                     // Feed Tab
                     pageWithTopBar(
                         FeedPage(selecedTab: state.selectedTab)
@@ -83,6 +101,10 @@ struct MainPage: StateView {
                     .zIndex(1000)
                 }
             }
+            .onReceive(tabReselectionPublisher) { tappedTab in
+                // Dispatch action for all tab taps (including same-tab taps)
+                dispatch(TabbarClickAction(selectedTab: tappedTab))
+            }
             .navigationBarHidden(true)
         }
     }