ci(ios): install CocoaPods and build the workspace

The iOS job still built iosApp.xcodeproj without running pod install, so
Xcode couldn't find the Pods xcconfig and file lists (iosApp/Pods/ is
gitignored) and the build failed. Install the pods from Podfile.lock
(cached on it) and build iosApp.xcworkspace.

.github/workflows/spotube-release-binary.yml

@@ -659,6 +659,16 @@ jobs:
       - name: Make gradlew executable
         run: chmod +x gradlew
 
+      # MobileVLCKit comes from CocoaPods; iosApp/Pods/ is gitignored and the workspace needs it.
+      - name: Cache CocoaPods
+        uses: actions/cache@v6
+        with:
+          path: iosApp/Pods
+          key: pods-${{ runner.os }}-${{ hashFiles('iosApp/Podfile.lock') }}
+
+      - name: Install CocoaPods dependencies
+        run: pod install --deployment --project-directory=iosApp
+
       # Unsigned on purpose: there is no Apple developer account in CI. The IPA is meant for sideloading
       # (AltStore, Sideloadly, ...), which re-signs it with the user's own certificate.
       # The Gradle build phase inside Xcode reads these as project properties.
@@ -668,7 +678,7 @@ jobs:
           ORG_GRADLE_PROJECT_buildNumber: ${{ github.run_number }}
         run: >
           xcodebuild
-          -project iosApp/iosApp.xcodeproj
+          -workspace iosApp/iosApp.xcworkspace
           -scheme iosApp
           -configuration Release
           -sdk iphoneos