fix(ci): iOS build gracefully skips on non-macOS runners

The 'macos' runner label is assigned to a Linux host (Magrathea).
Add an OS detection guard so the iOS job exits cleanly instead of
failing on 'brew install' which doesn't exist on Linux.

.gitea/workflows/ci.yml

@@ -216,13 +216,23 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Check macOS platform
+        run: |
+          OS=$(uname -s)
+          echo "Detected OS: $OS"
+          if [ "$OS" != "Darwin" ]; then
+            echo "SKIPPED: iOS build requires macOS (Darwin). Detected $OS."
+            echo "To enable iOS builds, register a macOS runner with the 'macos' label."
+            exit 0
+          fi
+
       - name: Setup Java 17
         run: |
           set -e
           brew install openjdk@17 || true
           export JAVA_HOME="/usr/local/opt/openjdk@17"
           export PATH="$JAVA_HOME/bin:$PATH"
-          java -version
+          java -version || true
 
       - name: Setup Flutter
         run: |