docs: Update README to master index format

[apenlor]

Objective

This PR refactors the README.md on the main branch back into its "Master Index" format, following the merge of the Phase 2 feature branch.

Key Changes

• The detailed "Feature Chapter" documentation for Phase 2 has been replaced with a concise summary.
• The "Workshop Guide" table has been updated with direct links to the v2.0-observable-monolith tag and the merged Pull Request for Phase 2.
• The main "Running the Project" call-to-action link now points to the quick start guide for the new phase.

This brings the project's primary documentation into its final, correct state for this phase, serving as a clean entry point for the next phase of the lab.