fix(ci): skip on Gitea + add contents:write for release creation

- Add job condition `github.server_url == 'https://github.com'` so Gitea
  (no runner) ignores the workflow entirely
- Add `permissions: contents: write` required by softprops/action-gh-release

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

.github/workflows/release.yml

@@ -7,8 +7,11 @@ on:
 
 jobs:
   build:
+    if: github.server_url == 'https://github.com'
     runs-on: ubuntu-latest
     timeout-minutes: 60
+    permissions:
+      contents: write
 
     steps:
       - uses: actions/checkout@v4