ci(security): add Zizmor GitHub Actions workflow scanner

[dhc-tech]

Integrate Zizmor security scanner for static analysis of GitHub Actions workflows with SARIF reporting to GitHub Security & Quality dashboard.

Summary by Sourcery

Add automated security scanning for GitHub Actions workflows with Zizmor and GitHub Code Scanning integration.

Enhancements:

• Add automated Zizmor security auditing for GitHub Actions workflows, including weekly and workflow-change scans with findings surfaced through GitHub Code Scanning.

CI:

• Add a dedicated GitHub Actions workflow to run Zizmor and upload SARIF results to the Security & Quality dashboard.

[sourcery-ai]

Reviewer's Guide

Introduces a least-privilege, pinned GitHub Actions workflow that runs Zizmor against repository workflows on relevant changes and weekly, then uploads SARIF results to GitHub Security & Quality via Code Scanning.

Sequence diagram for the Zizmor workflow security scan

sequenceDiagram
    participant Trigger as Workflow trigger
    participant Actions as GitHub Actions
    participant Checkout as actions/checkout
    participant Zizmor as zizmor-action
    participant CodeScanning as GitHub Code Scanning

    Trigger->>Actions: Start zizmor workflow
    Actions->>Checkout: Checkout repository
    Checkout-->>Actions: Workflow files available
    Actions->>Zizmor: Run zizmor security audit
    Zizmor-->>Actions: Write results.sarif
    Actions->>CodeScanning: upload-sarif(results.sarif)
    CodeScanning-->>Actions: Publish findings to Security & Quality

Loading

File-Level Changes

Change	Details	Files
Add a dedicated GitHub Actions workflow to scan workflow definitions with Zizmor and publish SARIF findings to GitHub Code Scanning.	Trigger scans for workflow changes on main, pull requests targeting main, and a weekly scheduled run. Run the pinned Zizmor action with read-only checkout and request only the security-events permission needed for reporting. Generate a SARIF report and upload it under a dedicated zizmor Code Scanning category.	.github/workflows/zizmor.yml

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[sourcery-ai]

Hey - I've found 2 issues

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path=".github/workflows/zizmor.yml" line_range="42" />
<code_context>
+      - name: Run zizmor security audit
+        uses: woodruffw/zizmor-action@a87be7b233a0b8106f3634ea576ca22ebc29ffc1 # v1.4.1
+        with:
+          args: --format sarif .
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
</code_context>
<issue_to_address>
**issue (bug_risk):** When Zizmor finds a policy violation, the audit step exits nonzero and GitHub skips the subsequent `upload-sarif` step because it has the default `success()` condition, so the SARIF findings are not uploaded to Code Scanning.

**Triggers:** When the scanned workflows contain at least one Zizmor finding.

**Suggested fix:** Add `if: ${{ always() }}` to the SARIF upload step so the report is uploaded even when the audit step reports findings.
</issue_to_address>

### Comment 2
<location path=".github/workflows/zizmor.yml" line_range="46" />
<code_context>
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      security-events: write
+    steps:
+      - name: Check out repository
</code_context>
<issue_to_address>
**issue (bug_risk):** When this workflow runs for a pull request from a fork, GitHub downgrades the `GITHUB_TOKEN` to read-only despite `security-events: write`, so `upload-sarif` cannot write the Code Scanning result and the workflow fails with a resource-access error.

**Triggers:** When an external contributor opens a pull request that changes a workflow file.

**Suggested fix:** Skip SARIF uploading for fork pull requests, or use a separately trusted `pull_request_target` workflow that does not execute untrusted checkout contents.

```suggestion
      - name: Upload SARIF report to Code Scanning
        if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.fork == false
```
</issue_to_address>

Sourcery assessment

Needs a human reviewer. 2 findings to address first, and the workflow adds a pinned third-party action that executes with repository-read and security-events-write permissions and uploads scan findings to GitHub Code Scanning. A faulty scanner or action could produce incorrect or stale security results, but reverting stops future runs and the persisted findings can be cleared or regenerated.

Blocking findings: .github/workflows/zizmor.yml:42, .github/workflows/zizmor.yml:46

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