Scaffold backend: Hono + Rivet Kit + per-user Docker stack

Backend that provisions per-user OpenCode + Gitea Docker pair via
dockerode and exposes the Grow Agent / sub-agent Rivet Kit actors
described in the PRD. Sub-agent workflows route through the parent
Grow Agent's OpenCode Docker.

- src/docker/manager.ts spawns growqr-gitea-<userId> and growqr-opencode-<userId>
- src/actors/{grow-agent,sub-agent,registry}.ts: Rivet Kit actors
- src/routes/{actors,opencode,git}.ts: PRD section 5.2-5.4 HTTP API
- docker-compose.yml runs rivet-engine + backend (mounts host Docker socket)
- PRD updated to lock in per-user OpenCode/Gitea Docker topology

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -0,0 +1,101 @@
+# growqr-backend
+
+Backend for the Grow Agent Platform (see [`docs/PRD.md`](docs/PRD.md)).
+
+Per the PRD, every user gets:
+
+- A **Grow Agent** (Rivet Kit actor) that orchestrates **sub-agent actors**.
+- A **dedicated OpenCode Docker** container — every sub-agent workflow executes through it.
+- A **dedicated Gitea Docker** container — backs the agent's memory and project repos.
+- A frontend (Next.js, separate repo) that pulls the Rivet Kit React SDK and talks to the Grow Agent over the actor connection.
+
+## Architecture
+
+```
+  Frontend (Next.js + Rivet Kit React SDK)
+        │
+        ▼
+  Backend (Hono + Rivet Kit client + dockerode)
+        │
+        ├─▶ rivet-engine (compose service)  → Grow Agent + Sub-Agent actors
+        │
+        └─▶ Docker daemon (host)
+              ├─ growqr-gitea-<userId>     (one per user, spawned on demand)
+              └─ growqr-opencode-<userId>  (one per user, spawned on demand)
+```
+
+The backend mounts the host Docker socket so it can spawn the per-user
+container pair via `dockerode` on `POST /actors/provision`.
+
+## Layout
+
+```
+src/
+  config.ts              env config
+  log.ts                 pino logger
+  index.ts               Hono app entrypoint
+  docker/manager.ts      dockerode wrapper — spawns Gitea + OpenCode per user
+  actors/
+    grow-agent.ts        Rivet Kit master actor (one per user)
+    sub-agent.ts         Rivet Kit worker actor (workflows → OpenCode Docker)
+    registry.ts          Rivet Kit actor registry setup
+  routes/
+    actors.ts            PRD §5.2 — actor registry HTTP API
+    opencode.ts          PRD §5.3 — OpenCode Docker management
+    git.ts               PRD §5.4 — Gitea Docker management
+```
+
+## Local setup
+
+Prereqs: Node 22+, Docker, `docker compose`.
+
+```bash
+cp .env.example .env
+npm install
+docker compose up -d rivet-engine     # start Rivet engine
+npm run dev                            # start backend on :4000
+```
+
+The backend pulls the Gitea + OpenCode images on first user provision (no need to pre-pull).
+
+## Smoke test
+
+```bash
+# Provision a Grow Agent + spawn its OpenCode + Gitea Docker
+curl -X POST localhost:4000/actors/provision \
+  -H 'content-type: application/json' \
+  -d '{"userId":"u_alice"}'
+
+# Send a message
+curl -X POST localhost:4000/actors/u_alice/message \
+  -H 'content-type: application/json' \
+  -d '{"text":"hello"}'
+
+# Spawn a sub-agent
+curl -X POST localhost:4000/actors/u_alice/sub-agents \
+  -H 'content-type: application/json' \
+  -d '{"type":"coding","channelId":"ch-coding-1"}'
+
+# Run a workflow through OpenCode Docker
+curl -X POST localhost:4000/actors/u_alice/sub-agents/coding-<id>/run \
+  -H 'content-type: application/json' \
+  -d '{"prompt":"scaffold a Hello World"}'
+
+# Stop the user's stack
+curl -X POST localhost:4000/actors/u_alice/stop
+```
+
+`docker ps` should show `growqr-gitea-u_alice` and `growqr-opencode-u_alice` after provision.
+
+## What's stubbed
+
+These are wired structurally but not yet talking to real upstream APIs:
+
+- OpenCode HTTP/SSE session API (the `routes/opencode.ts` forwarder is a stub).
+- Gitea repo/commit calls (the `routes/git.ts` handlers are stubs).
+- Auth (PRD §5.1) and payments (PRD §5.5).
+- Persistent registry — currently in-memory; replace with a real DB.
+
+## Frontend
+
+The Next.js frontend lives at `../growqr-frontend` (currently cloned as a nested dir at `./growqr-frontend` — git-ignored from this repo). It will install `@rivetkit/react` and connect to the Grow Agent actor for chat + streaming events.