Augment Cosmos delegates system design to single agent

Handing off complete system designs to autonomous agents after design-doc sign-off shifts the engineering bottleneck from code generation/writing to high-level architecture design and automated diff reviews.

* Moving away from small, ticket-sized agent tasks reduces task fragmentation and alignment overhead for large projects.

* Human code reviewers verify the output against the approved design document in minutes rather than line-by-line coding reviews, increasing velocity.

* Production systems with thousands of active users can safely run code implemented this way, showing that well-defined specs reduce agent error rates.