Fix: grant contents:write permission to release workflow

GitHub's default GITHUB_TOKEN is read-only since 2023; the release
step needs contents:write to create releases and upload assets.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: matteo-campana

.github/workflows/build-release.yml

@@ -21,6 +21,8 @@ on:
 jobs:
   build:
     runs-on: windows-latest
+    permissions:
+      contents: write   # required to create GitHub releases and upload assets
 
     steps:
       # ── Checkout ────────────────────────────────────────────────