Triggering initial build fails

## Expected Behavior
Build should complete

## Actual Behavior
--- Step 14: Triggering Initial Builds ---
🤔 Would you like to trigger the initial builds for the frontend and backend now? (y/n)
y
➡️ Triggering backend build...
ERROR: (gcloud.builds.triggers.run) INVALID_ARGUMENT: source.revision must be specified to run this trigger

## Steps to Reproduce the Problem

1. Deploy following the wizard

Reproduce the deployment wizard through Step 14 and inspect the code that invokes the frontend and backend initial build triggers. Confirm the trigger run supplies the required source revision, then verify that both initial builds complete successfully.

Written by the indexing model from the issue text.