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.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

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+# continuum-backend
+
+Cloud control plane for Continuum. Bun + ElysiaJS, PostgreSQL (via pgCat/PgBouncer,
+with pgvector for frame embeddings), Redis Streams, and Cloudflare R2 storage.
+
+## Run
+
+```sh
+bun install
+cp .env.example .env   # fill in DATABASE_URL, REDIS_URL, R2_*, SUPABASE_JWT_SECRET
+bun run db:generate && bun run db:migrate
+bun run dev
+```
+
+## Layout
+
+- `src/db/` — Drizzle schema (`printers`, `farms`, `print_jobs`, `frame_embeddings`)
+  and client, pointed at pgCat.
+- `src/s3/` — R2 presigned URL helpers (`PUT` for client uploads, `GET` for the
+  edge proxy).
+- `src/queue/` — Redis client + `XADD` helper pushing onto `stream:camera_frames`
+  for `continuum-ai-worker`.
+- `src/routes/` — `/auth`, `/farms`, `/printers`, `/jobs`, and the edge-gateway
+  WebSocket at `/ws/edge/v1`.
+
+`frame_embeddings.embedding` requires the `vector` extension:
+`CREATE EXTENSION IF NOT EXISTS vector;`