docs: align README with v2 application framework

[codeforester]

Summary

• reposition the README lead around the v2 application framework and standard-library value proposition
• add a runnable declarative CLI/configuration/lifecycle example and execute it in the documentation contract
• organize the library map by foundation, building blocks, and application framework
• link the pinned Beacon v0.1.2 learning path consistently

Validation

• ./tests/docs-contract.sh
• git diff --check
• shellcheck --severity=warning --shell=bash tests/docs-contract.sh

Fixes #569