chore: readme update

[dhfang]

Updates the repo readme to reflect the presence of new monorepo components

closes FOU-1222

[greptile-apps]

Greptile Summary

Updates the repository README to reflect the expanded monorepo structure and improve documentation discovery.

• Revises the project title and synopsis.
• Adds a repository-layout table covering specifications, CLI, documentation, tests, protobufs, generated code, examples, and scripts.
• Adds direct links to introductory, architecture, and CLI documentation.

Confidence Score: 5/5

The documentation-only change appears safe to merge.

The updated component descriptions are consistent with their repository contents, all referenced paths exist, and no blocking or independently actionable issue remains.

Important Files Changed

Filename	Overview
README.md	The revised repository overview, component descriptions, and documentation links align with the current tree; all relative links resolve.

_{Reviews (1): Last reviewed commit: "reword the repository layout and documen..." | Re-trigger Greptile}

[linear-code]

FOU-1222