ci(infra): add top-level permissions and SHA-pin third-party actions [INF-0000] (#35588)

## Summary

- Adds top-level `permissions: contents: read` to 5 workflows that only
had job-level permissions: `pr_labeler_file`, `pr_labeler_title`,
`tag-external-contributions`, `v03_api_doc_build`,
`auto-label-by-package`
- SHA-pins all 14 third-party actions to full commit SHAs to prevent
supply chain attacks via tag hijacking

## Why

**Missing top-level permissions:** Without an explicit top-level
`permissions` block, workflows inherit the repository/org default token
permissions, which may be overly broad. Adding `contents: read` as the
default restricts the blast radius if a dependency or action step is
compromised.

**SHA pinning:** Mutable tags (`@v1`, `@master`) can be force-pushed by
the action maintainer or an attacker who compromises their account.
Pinning to a full 40-character SHA ensures the exact reviewed code
always runs. Tag comments are preserved for readability.

### Actions pinned

| Action | File(s) |
|--------|---------|
| `pypa/gh-action-pypi-publish` | `_release.yml` (2 uses) |
| `ncipollo/release-action` | `_release.yml` |
| `Ana06/get-changed-files` | `check_diffs.yml` |
| `astral-sh/setup-uv` | `check_diffs.yml`, `uv_setup/action.yml` |
| `CodSpeedHQ/action` | `check_diffs.yml` |
| `google-github-actions/auth` | `integration_tests.yml` |
| `aws-actions/configure-aws-credentials` | `integration_tests.yml` |
| `amannn/action-semantic-pull-request` | `pr_lint.yml` |
| `bcoe/conventional-release-labels` | `pr_labeler_title.yml` |
| `mikefarah/yq` | `v03_api_doc_build.yml` |
| `EndBug/add-and-commit` | `v03_api_doc_build.yml` |
| `peter-evans/create-pull-request` | `refresh_model_profiles.yml` |

## Test plan

- [x] CI passes — all workflows still resolve their actions correctly
- [x] Verify no functional change: SHA refs point to the same code as
the previous tags

---

> This PR was generated with assistance from an AI coding agent as part
of a repository posture check.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.github/actions/uv_setup/action.yml

@@ -27,7 +27,7 @@ runs:
   using: composite
   steps:
     - name: Install uv and set the python version
-      uses: astral-sh/setup-uv@v7
+      uses: astral-sh/setup-uv@0ca8f610542aa7f4acaf39e65cf4eb3c35091883 # v7
       with:
         version: ${{ env.UV_VERSION }}
         python-version: ${{ inputs.python-version }}