chore: set static deployment URL for github-pages environment

Use the canonical domain instead of the dynamic page_url output
so the environment link in GitHub always points to weekly.codetengu.com.

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

Author: vinta

.github/workflows/deploy.yml

@@ -17,7 +17,7 @@ jobs:
   deploy:
     environment:
       name: github-pages
-      url: ${{ steps.deployment.outputs.page_url }}
+      url: https://weekly.codetengu.com/
     runs-on: ubuntu-latest
     steps:
       - name: Checkout