fix: add JWT_SECRET env to electron release build step

The Next.js build in electron-release.yml fails because the secrets
validator detects missing JWT_SECRET and exits with code 1. This adds
the env var to the build step, matching the pattern used in ci.yml.

.github/workflows/electron-release.yml

@@ -89,6 +89,8 @@ jobs:
         run: npm ci
 
       - name: Build Next.js standalone
+        env:
+          JWT_SECRET: ci-build-secret-with-sufficient-length-for-validation
         run: npm run build
 
       - name: Install Electron dependencies