feat: OTA四层架构 — manifest.json统一+渠道默认stable

- manifest.json: stable/beta/nightly三渠道H5+APK统一
- version.txt: 指向manifest.json URL
- v5嵌入页: channel默认stable, localStorage.channel可切换
- Bridge.fetchManifest: 自动读manifest.json解析对应渠道
- index-stable/beta/nightly: 业务页(开发期beta/nightly→stable)
- 删除旧版index-v6/v7
- 构建成功

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

@@ -62,21 +62,21 @@ class MainActivity : AppCompatActivity() {
             return digest.joinToString("") { "%02x".format(it) }
         }
 
-        /** Fetch manifest JSON from Gitea — proxy to avoid CORS in WebView */
+        /** Fetch manifest JSON from Gitea and return channel's section */
         @android.webkit.JavascriptInterface
         fun fetchManifest(channel: String): String {
-            val url = "https://git.childish-ghost.com/LukeMackin/Yuzu-GCA/raw/branch/main/ota/h5-manifest-$channel.json"
-            Log.i(TAG, "Bridge fetching $url")
+            val manifestUrl = "https://git.childish-ghost.com/LukeMackin/Yuzu-GCA/raw/branch/main/ota/manifest.json"
+            Log.i(TAG, "Bridge fetching $manifestUrl → $channel")
             return try {
-                val conn = URL(url).openConnection() as HttpURLConnection
-                conn.connectTimeout = 10_000
-                conn.readTimeout = 10_000
+                val conn = URL(manifestUrl).openConnection() as HttpURLConnection
+                conn.connectTimeout = 10_000; conn.readTimeout = 10_000
                 conn.instanceFollowRedirects = true
-                val code = conn.responseCode
-                if (code != 200) throw Exception("HTTP $code")
-                conn.inputStream.bufferedReader().readText()
+                if (conn.responseCode != 200) throw Exception("HTTP ${conn.responseCode}")
+                val raw = conn.inputStream.bufferedReader().readText()
+                val json = org.json.JSONObject(raw)
+                json.getJSONObject(channel).toString()
             } catch (e: Exception) {
-                Log.e(TAG, "Bridge fetch failed: ${e.message}")
+                Log.e(TAG, "Bridge fetchManifest($channel) failed: ${e.message}")
                 """{"error":"${e.message}"}"""
             }
         }