ci(lint): resolve uv packages via PYPI_MIRROR_URL pipeline variable

uv ignores pip.conf and hits pypi.org directly, stalling on CN cluster
runners. Point UV_INDEX_URL at the pipeline variable PYPI_MIRROR_URL
(value configured in Repository -> Pipeline -> Variables) instead of
hardcoding the internal hostname, which the open-source sensitive-info
scan rightly rejects for this mirrored-to-GitHub tree.

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

Sync-Source-Commit: 1e5edc082b2ea32ae9c7d36c6949c0754b192698
Ark-APIs-Commit: 59c90de5ac837a87443bd463e4500f6ef6eceda6
Hand-Written-Reason: Manual lint pipeline fix (route uv through PYPI_MIRROR_URL pipeline variable). No ark-apis regeneration involved; attributed to the same ark-apis snapshot as parent a4af56f.
Release-Version: 0.2.0

Author: ark-hand[bot]

.codebase/pipelines/python-lint-ci.yaml

@@ -11,6 +11,13 @@ jobs:
     image: python:3.12-slim
     runs-on:
       cluster:
+    envs:
+      # uv does not read pip.conf, so it resolves against pypi.org directly
+      # and times out from CN cluster runners. The mirror URL itself lives
+      # in Repository -> Pipeline -> Variables (PYPI_MIRROR_URL) so the
+      # internal hostname stays out of this mirrored-to-GitHub tree; pip is
+      # platform-configured and needs nothing.
+      UV_INDEX_URL: ${{PYPI_MIRROR_URL}}
     steps:
       - name: ruff lint and format check
         commands: