refactor(discord): remove rich presence and bundled SDK

Remove the presence setting, platform bridge, SDK archive, and SDK preparation from local and CI builds. Reject leftover Discord native libraries in release APK audits.

.github/workflows/release.yml

@@ -120,11 +120,6 @@ jobs:
           # Set NDK path
           echo "ANDROID_NDK_HOME=$ANDROID_HOME/ndk/29.0.14206865" >> "$GITHUB_ENV"
 
-      - name: Prepare pinned Discord SDK
-        uses: ./.github/actions/discord-sdk
-        with:
-          passphrase: ${{ secrets.DISCORD_SDK_PASSPHRASE }}
-
       - name: Setup Flutter
         uses: subosito/flutter-action@1a449444c387b1966244ae4d4f8c696479add0b2 # v2
         with:
@@ -209,9 +204,9 @@ jobs:
         run: |
           apk_dir=build/app/outputs/flutter-apk
           python3 scripts/check_backend_apk.py "$apk_dir/SpotiFLAC-${VERSION}-arm64.apk" \
-            --backend rust --abis arm64-v8a --require-discord
+            --backend rust --abis arm64-v8a
           python3 scripts/check_backend_apk.py "$apk_dir/SpotiFLAC-${VERSION}-arm32.apk" \
-            --backend rust --abis armeabi-v7a --require-discord
+            --backend rust --abis armeabi-v7a
           for abi in arm64 arm32; do
             "$ANDROID_HOME/build-tools/37.0.0/zipalign" -c -P 16 4 \
               "$apk_dir/SpotiFLAC-${VERSION}-${abi}.apk"