Simplify workflows: drop setup-node/pnpm-action, use corepack

The runner containers use node:20-bookworm which already has Node
and corepack. Remove actions/setup-node and pnpm/action-setup
which hang in Gitea Actions. Use corepack enable + pnpm directly.
Also fix preview comment to use Gitea API instead of github-script.

.gitea/workflows/deploy-preview.yaml

@@ -10,12 +10,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: pnpm/action-setup@v4
-
-      - uses: actions/setup-node@v4
-        with:
-          node-version: 20
-          cache: pnpm
+      - run: corepack enable && corepack prepare pnpm@latest --activate
 
       - run: pnpm install --frozen-lockfile
 
@@ -48,17 +43,11 @@ jobs:
           done
 
       - name: Comment preview URL
-        uses: actions/github-script@v7
-        with:
-          script: |
-            const { owner, repo } = context.repo;
-            const issue_number = context.issue.number;
-            const body = `## Preview Deploy\nNamespace: \`preview-${issue_number}\`\nArgoCD will sync automatically from branch \`${context.payload.pull_request.head.ref}\`.`;
-            await fetch(`${process.env.GITHUB_API_URL}/repos/${owner}/${repo}/issues/${issue_number}/comments`, {
-              method: 'POST',
-              headers: {
-                'Authorization': `token ${process.env.GITHUB_TOKEN}`,
-                'Content-Type': 'application/json'
-              },
-              body: JSON.stringify({ body })
-            });
+        env:
+          GITEA_TOKEN: ${{ gitea.token }}
+        run: |
+          curl -s -X POST \
+            -H "Authorization: token ${GITEA_TOKEN}" \
+            -H "Content-Type: application/json" \
+            -d "{\"body\": \"## Preview Deploy\nNamespace: \`preview-${{ gitea.event.number }}\`\nArgoCD will sync automatically.\"}" \
+            "${{ gitea.server_url }}/api/v1/repos/${{ gitea.repository }}/issues/${{ gitea.event.number }}/comments"