fix: ensure icons are RGBA PNG before build using imagemagick

.gitea/workflows/release.yml

@@ -127,7 +127,7 @@ jobs:
         run: |
           apt-get update
           apt-get install -y \
-            curl wget file gcc \
+            curl wget file gcc imagemagick \
             libwebkit2gtk-4.1-dev \
             libssl-dev \
             libxdo-dev \
@@ -137,6 +137,14 @@ jobs:
             xdg-utils \
             squashfs-tools
 
+      - name: Ensure icons are RGBA PNG
+        run: |
+          for f in src-tauri/icons/*.png; do
+            info=$(identify -verbose "$f" 2>/dev/null | grep "Type:" | head -1)
+            echo "$f: $info"
+            convert "$f" -type TrueColorAlpha PNG32:"$f"
+          done
+
       - name: Set up Rust toolchain
         run: |
           source "$HOME/.cargo/env" 2>/dev/null || true