fix(publish): uv pip install + bump 0.1.0a3 — v0.1.0a2 run died on missing pip

[qxbyte]

Repro

`git push origin v0.1.0a2` fired `publish-to-pypi` (run `26715540392`). All 15 publish jobs failed on:

```
Run uv venv --python ... /tmp/build-env
/tmp/build-env/bin/pip install build twine
##[error]Process completed with exit code 127.
```

Cause

Same bug PR #2 + PR #3 fixed for `bench.yml`: `uv venv` does not bootstrap `pip` into the venv. So `/tmp/build-env/bin/pip` doesn't exist. I missed mirroring the fix into `publish.yml` at the time.

Fix

```yaml

• name: Create isolated build venv
  run: |
  uv venv --python ${{ env.BUILD_PYTHON_VERSION }} /tmp/build-env
• /tmp/build-env/bin/pip install build twine

• uv pip install --python /tmp/build-env/bin/python build twine
  ```

Why bump 0.1.0a3 (not re-tag a2)

Re-tagging `v0.1.0a2` at the new commit:

• requires `git push --delete origin v0.1.0a2` (mild risk — protected branches generally don't lock tags, but it's still a forced operation)
• introduces `skip-existing` ambiguity if any upload in the failed run actually slipped through (I checked: none did, but bumping a3 is just cleaner)

So bump everyone to `0.1.0a3` and we get a fresh, clean run.

State after the failed run

• Nothing was uploaded to TestPyPI. Per-job logs show all 15 died before the `Build` step, well before the `Publish to TestPyPI` step.
• The 15 TestPyPI Trusted Publishers configured today have never been exercised — we still don't know whether the environment names / OIDC config are correct. This PR's tag will be the first real test.

Test plan

• 6 required test matrix checks pass
• Merge + tag `v0.1.0a3`
• Watch `publish-to-pypi` run:
  • `determine-target` outputs `target=testpypi`
  • All 15 publish jobs reach the `Publish to TestPyPI` step
  • All 15 OIDC exchanges succeed
  • TestPyPI shows `0.1.0a3` on all 15 project pages

🤖 Generated with Claude Code

[pronto-qxbyte]

PRonto 评审

PR: #5 fix(publish): uv pip install + bump 0.1.0a3
作者: @qxbyte
分支: fix/publish-yml-uv-pip -> main

概览

修复CI发布流程中uv venv未自动安装pip的问题，并统一升级插件版本。

问题清单

• ✅ 未发现明显问题

建议改进

• 无

【严重度】

• 🔴 P0：阻塞，必须修复才能合并
• 🟡 P1：建议，强烈建议修复
• 🟢 P2：提示，可选优化

本评审由 PRonto 经 MiMo 生成