Add --omit dev to frontend SBOM workflow

## Summary

`workflow-generate-frontend-sbom.yml` generates a production SBOM but includes devDependencies. Since devDependencies don't ship to production, they should be excluded for more accurate security scanning.

## Suggested fix

Add `--omit dev` to the `cyclonedx-npm` command, or expose it as an input parameter (e.g. `npm-omit`, defaulting to `dev`).

```diff
npx @cyclonedx/cyclonedx-npm package-lock.json \
--output-reproducible \
--package-lock-only \
+ --omit dev \
-v --sv "${CDX_SV}" \
-o sbom.json
```