refactor(local): replace LocalStack with MiniStack for AWS service emulation

[hibare]

Summary

Replaces LocalStack with MiniStack for local AWS service emulation. LocalStack Community Edition has been discontinued, requiring a migration to a maintained alternative. MiniStack is an open-source, MIT-licensed drop-in replacement that provides the same AWS service emulation with a lighter footprint.

https://blog.localstack.cloud/the-road-ahead-for-localstack/

What Changed

• Replaced localstack/localstack:4.14.0 with ministackorg/ministack:1.3.66 (pinned by multi-platform SHA256 digest)
• Renamed service, container, hostname, and volumes from localstack to ministack for consistency
• Renamed init script localstack-init.sh to ministack-init.sh
• Updated all AWS_ENDPOINT_URL references to use the new hostname
• Updated health check to use nc (curl/wget not available in MiniStack container; localhost does not resolve, so 127.0.0.1 is used)
• Removed SERVICES=dynamodb environment variable (MiniStack runs all services by default)
• Updated Go test harness in internal/testutil/containers.go to use MiniStack image
• Updated Makefile dev-deps target to reference the new service name
• Added MiniStack note to README documenting the migration

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Refactor (no functional changes)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Backward Compatibility

This change is transparent to developers. All existing make targets and docker compose commands continue to work. The endpoint URL, port (4566), and AWS SDK configuration remain unchanged.