docs: add platform-as-product repository review and roadmap

[tukue]

Motivation

• Provide a concrete Platform-as-a-Product assessment and implementation-oriented roadmap to move the repo from a documented target-state to a productized, consumable platform SDK and reference implementations.
• Make the review easily discoverable by linking it from the root README.md so internal developer teams can find guidance and golden-path recommendations.

Description

• Add docs/platform-product-repository-review-2026-04-08.md containing an executive summary, current-state risks, target-state architecture, concrete repository structure proposal, prioritized improvement plan, example standards, CI/CD workflow, developer journey, and adoption metrics.
• Update README.md to include a link to the new review under the Platform progress section.
• This is a documentation-only change and does not modify runtime infrastructure or stack code.

Testing

• Ran npm run build to compile TypeScript sources and the build succeeded.
• Ran npm run synth to synthesize the CDK app and the synth completed successfully with non-blocking warnings about Node/CDK runtime compatibility and an AWS SDK v2 runtime advisory.
• No new automated unit or integration tests were added in this PR; follow-up work should add CI policy gates (cdk-nag), unit/snapshot tests, and policy checks as recommended in the document.

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Codex Task

[amazon-q-developer]

Review Summary

This documentation-only PR successfully adds a comprehensive platform-as-product repository review and roadmap. The changes are well-structured and provide valuable strategic guidance.

Changes Overview

• README.md: Added link to new review document in Platform progress section
• New documentation: 290-line comprehensive review covering architecture, gaps, recommendations, and implementation roadmap

Validation

✅ No runtime code changes - documentation only
✅ No security concerns identified
✅ Build and synth operations confirmed successful per PR description
✅ Well-organized content with clear sections and actionable recommendations
✅ No blocking defects identified

The review document provides excellent strategic guidance for platform evolution with concrete improvement plans and examples. Ready to merge.

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