Initial boilerplate scaffold for continuum-backend

Bun + ElysiaJS control plane: Drizzle/Postgres schema (printers, farms,
print_jobs, pgvector frame_embeddings), R2 presigned URLs, Redis Streams
frame ingestion queue, REST routes, and the /ws/edge/v1 edge-gateway
WebSocket uplink.

src/db/schema/index.ts

@@ -0,0 +1,4 @@
+export * from "./farms";
+export * from "./printers";
+export * from "./print_jobs";
+export * from "./embeddings";