Publish opted-in form submissions to Kafka through Bus API

[jmgasper]

Form submissions can now opt in to downstream processing by including "kafka": true (or the exact string "true") alongside version and answers. After the submission commits, the service publishes its validated answers, form key/version, receipt identity, timestamp, member ID, and source page to form.submitted using the shared tc-bus-api-wrapper and Auth0 M2M configuration used by neighboring v6 services.

• Omitted/false flags preserve existing behavior. Successful HTTP receipts are unchanged.
• A separate SubmissionEvent delivery receipt preserves immutable submissions, serializes concurrent retries, and avoids republishing acknowledged deliveries. Failed delivery returns 503; retrying the same body/key resumes it, including after form retirement.
• Includes OpenAPI, API/operations documentation, example environment settings, and pinned wrapper/core-library dependencies. The shared library requires Git subdependencies to be enabled in pnpm; both Git dependencies are pinned to commits.

Deployment requires migration 20260928010000_submission_events, BUSAPI_URL pointing to the API /v6 base, and outbound AUTH0_URL, AUTH0_AUDIENCE, AUTH0_CLIENT_ID, and AUTH0_CLIENT_SECRET. ECS must expose these settings to the runtime task. There is no background retry worker; callers retry failed requests. Consumers must deduplicate by submissionId because a lost acknowledgement or crash between Bus API acceptance and receipt commit can cause redelivery.

Validation: frozen-lockfile install, Prisma validation and migration against disposable PostgreSQL 17, lint, build, typecheck, 36 unit tests, and 20 PostgreSQL integration tests all passed. Tests cover event contents, true/string-true and false/omitted flags, rejection paths, commit-before-publication, concurrent retries, flag conflicts, and delivery failure/retry after retirement. The compiled service also initialized the real wrapper successfully; outbound event calls in automated tests are mocked, so no shared Kafka messages were emitted.