ci: 恢复 DMG 背景图方案，生成含 Gatekeeper 指引的背景图，移除 README 方案

.github/workflows/release.yml

@@ -70,48 +70,6 @@ jobs:
           TAURI_SIGNING_PRIVATE_KEY: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
           TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY_PASSWORD }}
 
-      - name: Add README to DMG
-        run: |
-          DMG_PATH=$(ls tauri-app/src-tauri/target/universal-apple-darwin/release/bundle/dmg/*.dmg | head -1)
-          DMG_RW="/tmp/temp_rw.dmg"
-          MOUNT_POINT="/tmp/dmg_mount"
-
-          # 转换为可读写格式
-          hdiutil convert "$DMG_PATH" -format UDRW -o "$DMG_RW"
-
-          # 挂载可读写 DMG
-          mkdir -p "$MOUNT_POINT"
-          hdiutil attach "$DMG_RW" -mountpoint "$MOUNT_POINT" -nobrowse
-
-          # 复制 README.txt 到 DMG 根目录
-          cp tauri-app/src-tauri/README.txt "$MOUNT_POINT/"
-
-          # 卸载
-          hdiutil detach "$MOUNT_POINT"
-
-          # 删除原 DMG，转换回压缩只读格式
-          rm -f "$DMG_PATH"
-          hdiutil convert "$DMG_RW" -format UDZO -o "$DMG_PATH"
-
-          # 清理临时文件
-          rm -f "$DMG_RW"
-
-      - name: Re-sign DMG
-        working-directory: tauri-app
-        run: |
-          DMG_PATH=$(ls src-tauri/target/universal-apple-darwin/release/bundle/dmg/*.dmg | head -1)
-          rm -f "${DMG_PATH}.sig"
-          # 将私钥写入临时文件（strip 去掉首尾空白）
-          # 注意：这里用 PK 作为临时 env 名，避免 TAURI_SIGNING_PRIVATE_KEY 被 clap 自动读取
-          python3 -c "import os; open('/tmp/private.key','w').write(os.environ['PK'].strip())"
-          # 通过 TAURI_SIGNING_PRIVATE_KEY_PATH 环境变量指定私钥文件，避免与 --private-key 冲突
-          npx tauri signer sign -p "$TAURI_SIGNING_PRIVATE_KEY_PASSWORD" "$DMG_PATH"
-          rm -f /tmp/private.key
-        env:
-          PK: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
-          TAURI_SIGNING_PRIVATE_KEY_PATH: /tmp/private.key
-          TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY_PASSWORD }}
-
       - name: Upload artifacts
         uses: actions/upload-artifact@v4
         with: