fix(generate): send native-deployment required_contexts as a JSON array

[joshua-temple]

Problem

The native GitHub Deployments create step passed required_contexts via gh api --raw-field required_contexts='[]'. --raw-field (and --field) always transmit the value as a scalar string, so GitHub received the literal "[]" and rejected the create with HTTP 422: For 'properties/required_contexts', "[]" is not an array or null. The Deployment was never created, and the follow-on in_progress/status calls then 404'd on an empty deployment id.

The step is gated to real GitHub (server_url == 'https://github.com') and non-dry-run, so act/gitea and the non-native lanes never exercised it. The live fleet (cascade-example-dryrun lane) caught it on the seed-dev orchestrate, a real non-dry-run run.

Fix

Assemble the create-deployment request body as JSON and pipe it via gh api --input - so required_contexts is a real, explicit empty array:

deployment_id=$(printf '{"ref":"%s","environment":"%s","auto_merge":false,"required_contexts":[],"auto_inactive":false}' "${{ github.sha }}" "$ENV_NAME" \
  | gh api repos/${{ github.repository }}/deployments \
    --method POST \
    --input - \
    --jq '.id')

The explicit [] is preserved deliberately: it means the deployment is not gated on any status contexts. Omitting the field would instead make GitHub apply the repository's default required contexts, a different and potentially blocking behavior. The in_progress and status steps are unchanged; they were only 404'ing because the create failed.

Verification

• New generator test TestNativeDeployments_RequiredContextsIsJSONArray (red before, green after): asserts the string form required_contexts='[]' is gone and a real "required_contexts":[] array plus --input - are emitted.
• Emitted shell verified with bash -n; the JSON body verified to parse with a real empty array.
• e2e scenario 31-native-deployments updated to assert the JSON-body create step and a not_contains guard against the rejected string form.
• go build, go test (3655 pass), go test -race, golangci-lint run all clean; e2e module builds and vets clean.

The real-GitHub 422 is only provable on the live fleet; cascade-example-dryrun is the runtime proof.