fix: route workflow_dispatch inputs through env vars to prevent template injection (template-injection)

[planetf1]

Summary

Tracked from #331 (zizmor CI gate). PR #1530 introduced zizmor enforcement and found that dispatch-to-contribs.yml uses ${{ github.event.inputs.version }} directly inside run: blocks, which is a template injection vector.

The workflow is workflow_dispatch and release-triggered only — no external attacker can trigger it without maintainer write access. The practical risk is low (requires insider intent or a compromised maintainer account), but the fix is mechanical and eliminates the issue entirely.

Affected locations

File	Lines	Expression
dispatch-to-contribs.yml	33–34	${{ github.event.inputs.version }} in version-resolve run: block
dispatch-to-contribs.yml	59	${{ steps.version.outputs.version }} in dispatch run: block (low confidence)

Fix

Route template expressions through environment variables per the AGENTS.md convention:

# Before (vulnerable)
run: |
  if [ -n "${{ github.event.inputs.version }}" ]; then
    VERSION="${{ github.event.inputs.version }}"

# After (safe)
env:
  INPUT_VERSION: ${{ github.event.inputs.version }}
run: |
  if [ -n "${INPUT_VERSION}" ]; then
    VERSION="${INPUT_VERSION}"

zizmor --fix can generate the corrected form automatically.

Definition of done

1. Route all template expressions in run: blocks through env: vars
2. Remove the template-injection entries from .github/zizmor.yml
3. zizmor reports no template-injection findings in dispatch-to-contribs.yml