Augment-It Workspace — Walking Skeleton Plan

First buildable plan for the augment-it rewrite. Scaffold @augment-it/workspace (Svelte 5 singleton, per the pre-flight spec) plus a thin Workspace Service container (Node/Fastify) plus one domain microservice (row-store) plus a NATS message bus. Browser ↔ Workspace Service is WebSocket; Workspace Service ↔ domain services is NATS pub/sub. Two spreadsheets become the proof-of-life payload: load → row appears in workspace state → invoke a capability → round-trip the change back through SSE-equivalent broadcast. Supersedes the Transport decision in [[Walking-Skeleton-Pre-Flight-Decisions]]; the demo audience (a 26-product client) is the reason.