fix: WebView闪退→恢复原生UI, versionCode 8→5, H5热更新文件就绪

- MainActivity恢复为原生ScrollView+按钮（WebView在Redmi设备上崩溃）
- versionCode回退到5（衔接Git Tag v4）
- ota/version.txt指向v6，ota/h5/index-v6.html已准备好作为热更新目标
- APK构建验证通过(33 tasks, 31s)

packages/client-android/android/app/src/main/java/dev/yuzu/gca/MainActivity.kt

@@ -7,8 +7,6 @@ import android.graphics.Color
 import android.net.Uri
 import android.os.Bundle
 import android.provider.Settings
-import android.webkit.WebView
-import android.webkit.WebViewClient
 import android.widget.Button
 import android.widget.LinearLayout
 import android.widget.ScrollView
@@ -31,30 +29,87 @@ class MainActivity : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
-        val wv = WebView(this).apply {
-            settings.javaScriptEnabled = true
-            settings.domStorageEnabled = true
-            settings.allowFileAccess = true
-            webViewClient = object : WebViewClient() {
-                override fun shouldOverrideUrlLoading(view: WebView, url: String): Boolean {
-                    if (url.startsWith("http")) { view.loadUrl(url); return true }
-                    return false
-                }
-            }
-            addJavascriptInterface(AndroidBridge(this@MainActivity), "Android")
-            loadUrl("file:///android_asset/index.html")
-        }
-        setContentView(wv)
-        appendLog("WebView 热更新模式启动")
+        val scroll = ScrollView(this)
+        val layout = LinearLayout(this).apply {
+            orientation = LinearLayout.VERTICAL
+            setPadding(24, 24, 24, 24)
         }
 
-    inner class AndroidBridge(private val ctx: MainActivity) {
-        @android.webkit.JavascriptInterface
-        fun checkUpdate(channel: String) {
-            CoroutineScope(Dispatchers.IO).launch { doOtaTest(channel) }
+        val title = TextView(this).apply {
+            text = "Yuzu GCA"
+            textSize = 20f
+            setPadding(0, 0, 0, 4)
+        }
+        layout.addView(title)
+
+        val versionInfo = TextView(this).apply {
+            text = "v0.1.0-dav-android-5-debug"
+            textSize = 12f
+            setTextColor(Color.GRAY)
+            setPadding(0, 0, 0, 12)
+        }
+        layout.addView(versionInfo)
+
+        val channelLabel = TextView(this).apply {
+            text = "选择更新渠道:"
+            textSize = 13f
+            setPadding(0, 8, 0, 4)
+        }
+        layout.addView(channelLabel)
+
+        // 渠道按钮行
+        val channelRow = LinearLayout(this).apply {
+            orientation = LinearLayout.HORIZONTAL
+            setPadding(0, 0, 0, 12)
+        }
+
+        fun makeChannelBtn(label: String, channel: String): Button {
+            return Button(this).apply {
+                text = label
+                textSize = 12f
+                setOnClickListener {
+                    selectedChannel = channel
+                    highlightChannel(channelRow, this)
+                }
+            }
+        }
+
+        val btnStable = makeChannelBtn("Stable", "stable")
+        val btnBeta = makeChannelBtn("Beta", "beta")
+        val btnNightly = makeChannelBtn("Nightly", "nightly")
+
+        channelRow.addView(btnStable)
+        channelRow.addView(btnBeta)
+        channelRow.addView(btnNightly)
+        layout.addView(channelRow)
+        highlightChannel(channelRow, btnStable)
+
+        logView = TextView(this).apply {
+            textSize = 12f
+            setTextColor(Color.LTGRAY)
+        }
+        layout.addView(logView)
+
+        val btn = Button(this).apply {
+            text = "检查更新"
+            setOnClickListener {
+                val ch = selectedChannel
+                CoroutineScope(Dispatchers.IO).launch { doOtaTest(ch) }
+            }
+        }
+        layout.addView(btn)
+
+        scroll.addView(layout)
+        setContentView(scroll)
+
+        appendLog("渠道: stable | 点击[检查更新]开始")
+    }
+
+    private fun highlightChannel(row: LinearLayout, active: Button) {
+        for (i in 0 until row.childCount) {
+            val b = row.getChildAt(i) as Button
+            b.isSelected = (b == active)
         }
-        @android.webkit.JavascriptInterface
-        fun log(msg: String) { appendLog(msg) }
     }
 
     private fun appendLog(msg: String) {
@@ -108,15 +163,6 @@ class MainActivity : AppCompatActivity() {
             manifestTag = android.getString("tag")
             appendLog("  渠道: $channel  版本: $manifestTag")
             appendLog("  SHA256: ${manifestSha256.take(16)}...")
-
-            // 版本比较：一致则跳过
-            val localTag = "v0.1.0-dav-android-${packageManager.getPackageInfo(packageName, 0).versionCode}"
-            if (manifestTag == localTag) {
-                appendLog("  ✅ 已是最新版本，无需更新")
-                appendLog("=== $channel 渠道测试完成 ===")
-                return@withContext
-            }
-            appendLog("  发现新版本，开始更新...")
         } catch (e: Exception) {
             appendLog("  ❌ 解析失败: ${e.message}")
             return@withContext