fix(release): don't feed empty signing env to electron-builder

When the signing secrets are absent, `CSC_LINK`/`APPLE_*`/`WIN_CSC_*` render
as empty strings. electron-builder treats a present (even empty) CSC_LINK as
"a certificate is configured", tries to load it, resolves the empty path to
the working dir and dies with "<workdir> not a file" — which broke the v0.4.0
release build.

Drop those env vars from the release build step so unsigned builds behave
exactly like the (already-green) dev build, which only sets
CSC_IDENTITY_AUTO_DISCOVERY=false. Add them back once an Apple Developer ID /
Windows cert is available.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/release-desktop.yml

@@ -162,14 +162,12 @@ jobs:
         working-directory: desktop
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # 未签名发布：故意不传 CSC_LINK / APPLE_* / WIN_CSC_* 这些 env。
+          # 当对应 secret 缺失时它们会被渲染成空字符串，而 electron-builder 一旦看到
+          # CSC_LINK 这个 key 就会进入证书签名流程，把空路径当成证书去加载，最终报
+          # "<workdir> not a file" 而失败。拿到 Apple Developer ID / Windows 证书后，
+          # 再把对应签名 env 加回来即可开启签名 + 公证。
           CSC_IDENTITY_AUTO_DISCOVERY: 'false'
-          CSC_LINK: ${{ secrets.MACOS_CERTIFICATE }}
-          CSC_KEY_PASSWORD: ${{ secrets.MACOS_CERTIFICATE_PASSWORD }}
-          APPLE_ID: ${{ secrets.APPLE_ID }}
-          APPLE_APP_SPECIFIC_PASSWORD: ${{ secrets.APPLE_APP_SPECIFIC_PASSWORD }}
-          APPLE_TEAM_ID: ${{ secrets.APPLE_TEAM_ID }}
-          WIN_CSC_LINK: ${{ secrets.WINDOWS_CERTIFICATE }}
-          WIN_CSC_KEY_PASSWORD: ${{ secrets.WINDOWS_CERTIFICATE_PASSWORD }}
         run: bunx electron-builder ${{ matrix.builder_args }} --publish never
 
       - name: Verify packaged app structure