Add Terraform setup for Lightsail Container Service

[Subhransu-De]

What to build

Add a Terraform infrastructure setup under /infra that deploys this FastAPI template using Amazon Lightsail Container Service. This setup should serve as the simplest AWS container option for small apps, demos, and users who want less infrastructure surface area than ECS.

The setup should deploy the FastAPI container, expose it through the Lightsail public endpoint, and document the expected tradeoffs compared with ECS.

Acceptance criteria

• Terraform provisions a Lightsail container service for the FastAPI app.
• The service supports configurable power, scale, container image, port, and health check path.
• App environment variables are configurable.
• Secret handling is documented clearly, including any limitations compared with ECS task secrets.
• Outputs include the Lightsail service name and public endpoint URL.
• Documentation explains image publishing requirements for Lightsail.
• Documentation compares when to use Lightsail Containers versus ECS Express Mode or ECS Fargate.
• A verification command is documented for checking the deployed health endpoint.

Blocked by

None - can start immediately.