[SHIP-1981]: Use ECR images for ECS deployment

[adriantaut]

Summary

• Use EcrContainerImage from @zarpay/zar-cdk-lib to pull images from ECR
• Update deploy.yml to build image and trigger infra deployment
• Make infra-deploy.yml a reusable workflow (supports both workflow_call and workflow_dispatch)
• Pass imageVersion via CDK context (--context imageVersion=<tag>)

Changes

• service.ts: Use EcrContainerImage.fromContext() instead of hardcoded GHCR image
• deploy.yml: Build + push image, then call infra-deploy.yml with image tag
• infra-deploy.yml: Reusable workflow with required imageVersion input
• infra-ci.yml: Pass dummy imageVersion for synth validation

Deployment Flow

Push to main → deploy.yml:
  1. Build job: builds image, tags as short SHA (e.g., abc1234)
  2. Deploy job: calls infra-deploy.yml with imageVersion=abc1234
       → CDK diff/deploy with --context imageVersion=abc1234
       → ECS pulls from ECR: 340458174631.dkr.ecr.me-central-1.amazonaws.com/fizzy:abc1234

Test plan

• yarn build passes
• CDK synth works with --context imageVersion=<tag>
• Verify deploy workflow triggers infra-deploy correctly

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