migrate to hantim org and consolidate deploy secret name

- Update all references from timothykim/ to hantim/ org
- Rename DEPLOY_KEY to DEPLOY_SSH_KEY everywhere
- Update README to reference org-level secrets

.gitea/workflows/deploy-nginx.yml

@@ -13,6 +13,6 @@ jobs:
       - name: Deploy via SSH
         run: |
           mkdir -p ~/.ssh
-          echo "${{ secrets.DEPLOY_KEY }}" > ~/.ssh/deploy_key
+          echo "${{ secrets.DEPLOY_SSH_KEY }}" > ~/.ssh/deploy_key
           chmod 600 ~/.ssh/deploy_key
           ssh -o StrictHostKeyChecking=accept-new -i ~/.ssh/deploy_key deploy@${{ secrets.DEPLOY_HOST }} deploy-nginx