Feat/serverless backend lambda

[MarcoManduca]

No description provided.

[Copilot]

Pull request overview

This PR migrates the backend runtime from ECS Fargate + ALB to a container-image AWS Lambda exposed via a Lambda Function URL and fronted by the existing CloudFront distribution, while also introducing a DynamoDB-backed contact-form rate limiter to make rate limiting consistent across Lambda cold starts.

Changes:

• Replace the ECS/ALB backend stack with a Lambda container image + Function URL, and route /api/* to it via CloudFront OAC (SigV4).
• Add a new DynamoDB TTL table for rate limiting and switch the backend limiter implementation to DynamoDB.
• Update Terraform variables/outputs plus deployment/local-dev scripts and documentation to match the new architecture.

Reviewed changes

Copilot reviewed 27 out of 27 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
README.md	Updates top-level architecture diagram and hosting stack description to Lambda.
infra/terraform/variables.tf	Replaces ECS sizing vars with Lambda memory/timeout vars.
infra/terraform/terraform.tfvars.example	Updates example backend sizing inputs for Lambda.
infra/terraform/providers.tf	Removes the random provider requirement (no longer used).
infra/terraform/outputs.tf	Replaces ECS/ALB outputs with the backend Lambda function name output.
infra/terraform/modules/database/outputs.tf	Exposes the new ratelimit table name/ARN via module outputs.
infra/terraform/modules/database/main.tf	Adds the DynamoDB ratelimit table with TTL enabled.
infra/terraform/modules/cdn/variables.tf	Replaces ALB origin variables with Lambda Function URL host + function name inputs.
infra/terraform/modules/cdn/main.tf	Switches /api/* origin to Lambda Function URL via OAC and adds invoke permission.
infra/terraform/modules/backend/variables.tf	Replaces ECS-related vars with Lambda-oriented configuration (arch/memory/timeout).
infra/terraform/modules/backend/outputs.tf	Exposes Lambda function name and Function URL host instead of ECS/ALB details.
infra/terraform/modules/backend/main.tf	Implements Lambda function + Function URL + log group, removing ECS/ALB runtime.
infra/terraform/modules/backend/iam.tf	Replaces ECS task/execution roles with a single Lambda execution role + policy.
infra/terraform/modules/backend/ecs.tf	Removes ECS cluster/task/service resources (deleted).
infra/terraform/modules/backend/alb.tf	Removes ALB/cert/DNS/origin-secret resources (deleted).
infra/terraform/main.tf	Rewires modules for Lambda backend + passes new env var for rate limit table.
infra/scripts/deploy-backend.sh	Updates deploy script to aws lambda update-function-code and arm64 builds.
infra/scripts/create-local-tables.sh	Adds creation of the local ratelimit DynamoDB table.
infra/README.md	Updates infra docs/runbook/diagrams and provisioning steps for Lambda + Function URL.
docker-compose.yml	Adds RATELIMIT_TABLE_NAME env var for local services.
backend/tests/unit/utils/test_rate_limit.py	Replaces in-memory limiter tests with moto-backed DynamoDB limiter tests.
backend/tests/conftest.py	Adds ratelimit table env + test table creation.
backend/src/utils/rate_limit.py	Replaces in-memory limiter with DynamoDB-backed fixed-window limiter + dependency.
backend/src/config.py	Adds ratelimit_table_name setting/env mapping.
backend/README.md	Updates backend documentation for Lambda runtime + DynamoDB-backed rate limiting.
backend/Dockerfile	Adds AWS Lambda Web Adapter extension and readiness configuration.
backend/.env.example	Adds RATELIMIT_TABLE_NAME and updates rate-limit docs.

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