Use existing PyPI mirror in Gitea CI

.gitea/workflows/backend-quality-gate.yml

@@ -155,6 +155,8 @@ jobs:
           docker image inspect "$POSTGRES_TEST_IMAGE" >/dev/null
 
       - name: Install dependencies
+        env:
+          PIP_INDEX_URL: https://mirrors.aliyun.com/pypi/simple/
         run: |
           set -euo pipefail
           python3 -m venv .venv

frontend/tests/staging-backend-workflows.test.ts

@@ -130,6 +130,7 @@ test("Gitea quality gate validates before publishing an immutable ACR manifest",
   assert.equal((workflow.match(/git clean -ffdx/g) ?? []).length, 2);
   assert.equal((workflow.match(/git status --porcelain --untracked-files=all/g) ?? []).length, 2);
   assert.match(workflow, /python3 -m venv \.venv/);
+  assert.match(workflow, /PIP_INDEX_URL: https:\/\/mirrors\.aliyun\.com\/pypi\/simple\//);
   for (const constraint of [
     'mcp==1.28.1',
     'pydantic==2.13.4',