Add postinst script to place desktop icon on install

Introduces a debian/postinst script in the build workflow to copy the ytsage.desktop file to the user's desktop during DEB package installation, ensuring the desktop icon is available. Also updates the icon cache and handles cases where the desktop directory or SUDO_USER is not set.

.github/workflows/build-linux.yml

@@ -125,6 +125,7 @@ jobs:
                 ("assets", "assets"),
                 ("ytsage.desktop", "share/applications/ytsage.desktop"),
                 ("assets/branding/icons/icon.png", "share/pixmaps/ytsage.png"),
+                ("debian/postinst", "DEBIAN/postinst"),  # Added for desktop icon
             ],
         )
 
@@ -174,6 +175,32 @@ jobs:
         StartupWMClass=YTSage
         DESKTOP
 
+    - name: Create postinst script for desktop icon
+      shell: bash
+      run: |
+        mkdir -p debian
+        cat > debian/postinst <<'POSTINST'
+        #!/bin/sh
+        set -e
+        # Copy .desktop file to user's desktop for icon
+        if [ -n "$SUDO_USER" ]; then
+          DESKTOP_DIR="/home/$SUDO_USER/Desktop"
+          if [ -d "$DESKTOP_DIR" ]; then
+            cp /usr/share/applications/ytsage.desktop "$DESKTOP_DIR/"
+            chmod +x "$DESKTOP_DIR/ytsage.desktop"
+            chown $SUDO_USER:$SUDO_USER "$DESKTOP_DIR/ytsage.desktop"
+            echo "Placed ytsage.desktop on $SUDO_USER's desktop"
+          else
+            echo "Warning: Desktop directory $DESKTOP_DIR not found, skipping desktop icon placement"
+          fi
+        else
+          echo "Warning: SUDO_USER not set, skipping desktop icon placement"
+        fi
+        # Update icon cache
+        gtk-update-icon-cache -f /usr/share/icons/hicolor/ 2>/dev/null || true
+        POSTINST
+        chmod +x debian/postinst
+
     - name: Build AppImage, RPM and DEB
       shell: bash
       run: |