feat: hide foreground webapp when switching sidebar pages

app/src/main/java/top/yeij/hearth/MainActivity.kt

@@ -293,6 +293,12 @@ class MainActivity : Activity() {
             Log.d(TAG, "switchWebView: id=$id")
         }
 
+        override fun hideAll() {
+            contentWebViews.values.forEach { it.visibility = View.GONE }
+            currentVisibleId = null
+            Log.d(TAG, "hideAll: hidden ${contentWebViews.size} webviews")
+        }
+
         override fun goBack(): Boolean {
             val webView = currentVisibleId?.let { contentWebViews[it] }
             return if (webView != null && webView.canGoBack()) {

app/src/main/java/top/yeij/hearth/webview/JsBridge.kt

@@ -202,6 +202,16 @@ class JsBridge(
         Log.d("HearthBridge", "webReload called")
     }
 
+    // 隐藏所有内容 WebView（把前台 webapp 丢到后台，标签状态保留）
+    // Hide all content WebViews (send the foreground webapp to background,
+    // keeping the tab state) — called when the user switches pages via the sidebar
+    @android.webkit.JavascriptInterface
+    fun hideWebApps() {
+        val host = webAppHost ?: return
+        onMain { host.hideAll() }
+        Log.d("HearthBridge", "hideWebApps called")
+    }
+
     // 清单内存缓存：首次拉取成功后缓存，后续复用（避免 openWebApp 重复 I/O）
     // 空结果（离线失败）不缓存，下次调用重试拉取，避免空清单被永久缓存
     // In-memory manifest cache: cache only on a successful non-empty fetch (avoid

app/src/main/java/top/yeij/hearth/webview/WebAppHost.kt

@@ -35,4 +35,9 @@ interface WebAppHost {
     // 将标签状态推送到桌面 H5 顶栏
     // Push the tab state to the desktop H5 topbar
     fun syncTabs(tabs: List<Tab>)
+
+    // 隐藏所有内容 WebView（把前台 webapp 丢到后台，标签状态保留）
+    // Hide all content WebViews (send the foreground webapp to background,
+    // keeping the tab state)
+    fun hideAll()
 }