Motivation

• Amazon Linux 2 has reached end-of-life, so the serverless documentation and runner image should recommend and use a supported runtime.
• The release workflow should validate the actual runtime image used to build the Lambda ZIP to catch runtime regressions early.

Description

• Update the serverless docs in README.md to recommend the Amazon Linux 2023 custom runtime (provided.al2023).
• Change the Lambda runner image in lambda.Dockerfile from public.ecr.aws/lambda/provided:al2 to public.ecr.aws/lambda/provided:al2023.
• Add a release workflow step in .github/workflows/release.yml to build the runner Docker target (docker build -t sqlpage-lambda . -f lambda.Dockerfile --target runner) so the runtime image is validated during CI.
• Add an unreleased entry to CHANGELOG.md noting the runtime migration.

Testing

• Ran git diff --check to validate the patch format, which succeeded.
• Parsed .github/workflows/release.yml with YAML (Ruby) to ensure the workflow is valid, which succeeded.
• Verified there are no remaining provided:al2 / "Amazon Linux 2" references with rg, which succeeded.
• Attempted to run cargo check --locked --features lambda-web and local docker build to fully validate the Lambda build; these could not complete in the current environment because the available Rust toolchain is older than required for some build dependencies and Docker is not available.

Codex Task