Add test infrastructure and post-deploy validation stage to CDK pipeline

[StevenAskwith]

Add test infrastructure and post-deploy validation stage to CDK pipeline

Wires up a complete test pipeline covering CDK, pre-deploy unit tests, and post-deploy live validation.

CDK / pipeline changes

• Enable cdk-nag across the stack
• DremWebsiteDistributionDomainName and appsyncId promoted to public readonly CfnOutput on DremAppStack and InfrastructurePipelineStage
• PostDeployTests CodeBuild step added, sequenced after MainSiteDeployToS3, fetches live schema via appsync:GetIntrospectionSchema and runs npm run test:post-deploy

Test reporting

• JUnit XML reports wired up for all CodeBuild steps, visible in the CodeBuild test report console
• CDK test suite name fixed in jest-junit config (was reporting as undefined)

Pre-deploy tests

• Migrated raceTableConfig and deviceTableConfig tests from Jest to Vitest for consistency
• vitest/globals added to tsconfig.json types to fix tsc --noEmit failures on vi.* in test files

Post-deploy tests (16 new)

• GraphQL schema conformance (Layer 1) — validates all .ts and .js queries, mutations and subscriptions against the live AppSync schema
• Playwright smoke tests — HTTP 200, page title, #root element, env var sanity
• Dedicated vitest.config.post-deploy.ts to prevent vitest exclude list blocking explicitly named test files

Documentation

• docs/testing-strategy.md — full description of the test pipeline, what each layer covers, known gaps, and future directions
• README.md — Testing section added with link to testing strategy

Total pipeline test count: 57

Stage	Tests	Count
Pre-deploy (CDK)	CDK stack assertions	1
Pre-deploy (website)	Component/unit tests	40
Post-deploy	GraphQL schema conformance	12
Post-deploy	Smoke (HTTP 200, title, #root, env var)	4
Total		57