Automated indexer deployment with API endpoint under same domain

[koenmtb1]

Summary

• Add automated blue-green deployment for the Ponder indexer via two GitHub Actions workflows: one deploys to the slave color and exits, a cron (every 30 min) polls the new backend's sync status and switches over once ready
• Route /api/* requests through the frontend CloudFront distribution (stake.aztec.network/api/*) to the live indexer origin, eliminating the need for a separate API domain and frontend redeployments on indexer switchovers
• Add /api/sync-status endpoint that compares the indexer's max indexed block against the chain head, used by the cron to detect when re-indexing is complete
• Replace the 404 custom_error_response with a CloudFront Function for SPA routing, since custom_error_response is distribution-wide and would swallow API 404s

How it works

• Trigger Deploy Indexer (Blue-Green) workflow → deploys to the slave color (opposite of live), writes a pending switchover to S3, exits (~5 min)
• Check Indexer Sync cron runs every 30 min → hits /api/sync-status on the slave's CloudFront → if synced, updates the indexerOrigin on the frontend CloudFront via AWS CLI, clears the pending state, and triggers a deploy to the old live so both end up updated
• The frontend always hits /api/* on its own domain — CloudFront routes it to whichever indexer backend is live. No frontend redeploy needed for switchovers.

Setup
Run scripts/init-deployment-state.sh <environment> <live_color> once per environment to create the S3 state file before using the blue-green workflow.