fix(android): change QR scanner to portrait orientation

- Created PortraitCaptureActivity that extends CaptureActivity
- Registered it in AndroidManifest.xml with screenOrientation="portrait"
- Updated JoinKeygenScreen and CoSignJoinScreen to use the portrait activity
- Also simplified keygen join logic to match Electron exactly

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/mpc-system/services/service-party-android/app/src/main/AndroidManifest.xml

@@ -31,6 +31,14 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
+
+        <!-- Portrait-only QR code scanner activity -->
+        <activity
+            android:name=".presentation.screens.PortraitCaptureActivity"
+            android:screenOrientation="portrait"
+            android:stateNotNeeded="true"
+            android:theme="@style/zxing_CaptureTheme"
+            android:windowSoftInputMode="stateAlwaysHidden" />
     </application>
 
 </manifest>

backend/mpc-system/services/service-party-android/app/src/main/java/com/durian/tssparty/presentation/screens/CoSignJoinScreen.kt

@@ -168,7 +168,8 @@ fun CoSignJoinScreen(
                     setCameraId(0)
                     setBeepEnabled(true)
                     setBarcodeImageEnabled(false)
-                    setOrientationLocked(false)
+                    setOrientationLocked(true)
+                    setCaptureActivity(PortraitCaptureActivity::class.java)
                 }
                 scanLauncher.launch(options)
             },

backend/mpc-system/services/service-party-android/app/src/main/java/com/durian/tssparty/presentation/screens/JoinKeygenScreen.kt

@@ -220,6 +220,7 @@ private fun InputScreen(
                     setBeepEnabled(true)
                     setBarcodeImageEnabled(false)
                     setOrientationLocked(true)
+                    setCaptureActivity(PortraitCaptureActivity::class.java)
                 }
                 scanLauncher.launch(options)
             },

backend/mpc-system/services/service-party-android/app/src/main/java/com/durian/tssparty/presentation/screens/PortraitCaptureActivity.kt

@@ -0,0 +1,9 @@
+package com.durian.tssparty.presentation.screens
+
+import com.journeyapps.barcodescanner.CaptureActivity
+
+/**
+ * Portrait-only barcode capture activity
+ * Used to force the QR scanner to use portrait orientation
+ */
+class PortraitCaptureActivity : CaptureActivity()