build: one image, nginx in front of the backend on loopback (closes #52)

The root Dockerfile builds the only image; Dockerfile.backend is gone.
Its stages: lint, a Go stage that runs the tests and builds
netwatch-server, the node stage, and an nginx runtime. nginx serves
dist/ on 8080 and proxies /api/ and /.well-known/healthcheck to the
backend on 127.0.0.1:8081. bin/entrypoint.sh starts both, turns TERM or
INT into a stop of both, and exits non-zero when either exits on its
own. The backend runs as user netwatch and keeps reports on the /data
volume. New setting BIND_ADDRESS (empty: every interface). STOPSIGNAL is
SIGTERM, since the nginx image's SIGQUIT would miss the entrypoint.
script/docker is the org model verbatim.

Model: opus-5-5

backend/README.md

@@ -11,15 +11,16 @@ From this directory:
 make run
 ```
 
-From the repo root, which is also the build context of `Dockerfile.backend`:
+From the repo root, whose `Dockerfile` builds the one image that ships this
+backend behind nginx (see [Container image](#container-image)):
 
 ```bash
 # Run tests, lint, and format check over the frontend and this backend
 make check
 
-# Build both images, including netwatch-server
+# Build the image: nginx, the frontend and this backend
 make docker
-docker run -p 8080:8080 netwatch-server
+docker run -p 8080:8080 netwatch
 ```
 
 ## Entrypoints
@@ -27,7 +28,7 @@ docker run -p 8080:8080 netwatch-server
 This directory follows the same
 [Scripts to Rule Them All](https://github.com/github/scripts-to-rule-them-all)
 pattern as the repo root: the targets in `backend/Makefile` are thin shims over
-`backend/script/`. `Dockerfile.backend` runs them, and the root scripts call
+`backend/script/`. The root `Dockerfile` runs them, and the root scripts call
 `test`, `fmt` and `fmt-check`:
 
 - `script/build` — compile the static `netwatch-server` binary with its version
@@ -37,8 +38,8 @@ pattern as the repo root: the targets in `backend/Makefile` are thin shims over
 - `script/test` — run the Go tests under a 30-second timeout
 - `script/lint` — check `.golangci.yml` against its pinned sha256, then run
   golangci-lint. It runs inside the golangci-lint image of the lint stage of
-  `Dockerfile.backend`; from a checkout, run `make lint` at the repo root, which
-  builds that stage
+  the root `Dockerfile`; from a checkout, run `make lint` at the repo root,
+  which builds that stage
 - `script/fmt` — format the Go sources (writes)
 - `script/fmt-check` — check Go formatting (read-only)
 - `script/run` — build and run the server locally
@@ -46,7 +47,7 @@ pattern as the repo root: the targets in `backend/Makefile` are thin shims over
 
 There is no `check`, `hooks` or `docker` target here: the root `make check`
 covers this directory, the root `make hooks` installs the repo's only pre-commit
-hook, and the root `make docker` builds this image.
+hook, and the root `make docker` builds the image that contains this backend.
 
 ## Rationale
 
@@ -76,6 +77,7 @@ Internal packages in `internal/` follow standard Go project layout:
 
 | Variable          | Default              | Description                                                                                              |
 | ----------------- | -------------------- | -------------------------------------------------------------------------------------------------------- |
+| `BIND_ADDRESS`    | empty                | IP address to listen on; empty listens on every interface                                                |
 | `PORT`            | `8080`               | HTTP listen port                                                                                         |
 | `DATA_DIR`        | `./data/reports`     | Directory for compressed reports                                                                         |
 | `DEBUG`           | `false`              | Enable debug logging                                                                                     |
@@ -86,6 +88,15 @@ The loopback entries cover the reverse proxy that shares the container; the
 RFC1918 ranges match `nginx.conf`. A request whose direct peer is outside this
 set has its forwarded headers ignored, and the direct peer is logged instead.
 
+### Container image
+
+The root `Dockerfile` builds one image in which nginx listens on the public port
+8080, serves the frontend, and proxies `/api/` and `/.well-known/healthcheck` to
+this server. The image's entrypoint, `bin/entrypoint.sh`, starts the server as
+user `netwatch` (uid 1000) with `BIND_ADDRESS=127.0.0.1` and `PORT=8081`, so
+only nginx reaches it. `DATA_DIR` is `/data/reports`, on the `/data` volume,
+which `netwatch` owns.
+
 ### Report storage
 
 Reports are written as `reports-<timestamp>.jsonl.zst` files in `DATA_DIR`.