[PATCH pve_flutter_frontend] android: add taskAffinity attribute with empty string in MainActivity

[Shan Shaji <s.shaji@proxmox.com>]

On android vesions lower than 11, inorder to prevent Android Task
Hijacking (a.k.a, StrandHogg Attack [0][1]) `taskAffinity` attribute
was updated to empty string [0] for the flutter app template [2]. To
align with that and protect users running our app on older devices
(our `minSdkVersion` is 24) apply the same update here.

Note that StrandHogg v2 will still affect Android versions lower than
11, as the required OS level patches are only available from SDK level
30 [3].

- [0] https://github.com/flutter/flutter/issues/63559
- [1] https://developer.android.com/privacy-and-security/risks/strandhogg
- [2] https://github.com/flutter/flutter/pull/144018/changes
- [3] https://developer.android.com/privacy-and-security/risks/strandhogg#mitigations

Originally-by: Azharul Haque <haque@azharul.com>
Signed-off-by: Shan Shaji <s.shaji@proxmox.com>
---

 This came up while I was reviewing this change [0]. When I checked the
 install base on play console, we have 2,300 active install base for
 android versions less than 11.

 - [0] https://lore.proxmox.com/pve-devel/20260821034147.30194-10-haque@azharul.com/T/#u

 android/app/src/main/AndroidManifest.xml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/android/app/src/main/AndroidManifest.xml b/android/app/src/main/AndroidManifest.xml
index 66135eb..654f13d 100644
--- a/android/app/src/main/AndroidManifest.xml
+++ b/android/app/src/main/AndroidManifest.xml
@@ -12,6 +12,7 @@
             android:name="com.proxmox.app.pve_flutter_frontend.MainActivity"
             android:exported="true"
             android:launchMode="singleTop"
+            android:taskAffinity=""
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
             android:hardwareAccelerated="true"
--
2.47.3