refactor: rename Gitea environment variables to CI registry prefix

update SETUP.md and .env.example

.gitea/workflows/dependency-updates.yml

@@ -13,7 +13,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
-          token: ${{ secrets.GITEA_TOKEN }}
+          token: ${{ secrets.CI_REGISTRY_TOKEN }}
 
       - name: Setup Node.js
         uses: actions/setup-node@v4
@@ -42,7 +42,7 @@ jobs:
       - name: Create Pull Request
         uses: peter-evans/create-pull-request@v5
         with:
-          token: ${{ secrets.GITEA_TOKEN }}
+          token: ${{ secrets.CI_REGISTRY_TOKEN }}
           commit-message: "chore: update dependencies"
           title: "chore: weekly dependency updates"
           body: |