Move to the layout REPO_POLICIES.md gives (closes #30)

The Go module moves from backend/ to the root (go.mod, go.sum,
.golangci.yml, cmd/, internal/), the page's source to web/, and nginx's
two files to configs/. backend/ is gone: its LICENSE and .dockerignore
are deleted, and its .gitignore entries, README and scripts are folded
into the root ones. script/build builds the server binary after the
frontend; script/run and script/clean move up from backend/script/;
make test, lint, fmt and fmt-check do what the backend's did. Vite's
root is web/ and it still builds into dist/. script/bootstrap no longer
installs gcc, which only the host Go tests needed.

Model: opus-5-5

cmd/netwatch-server/main.go

@@ -0,0 +1,89 @@
+// Package main is the entry point for netwatch-server.
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+
+	"sneak.berlin/go/netwatch/internal/config"
+	"sneak.berlin/go/netwatch/internal/globals"
+	"sneak.berlin/go/netwatch/internal/handlers"
+	"sneak.berlin/go/netwatch/internal/healthcheck"
+	"sneak.berlin/go/netwatch/internal/logger"
+	"sneak.berlin/go/netwatch/internal/middleware"
+	"sneak.berlin/go/netwatch/internal/reportbuf"
+	"sneak.berlin/go/netwatch/internal/server"
+
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxevent"
+)
+
+//nolint:gochecknoglobals // set via ldflags at build time
+var (
+	Appname = "netwatch-server"
+	Version string
+)
+
+func main() {
+	// "netwatch-server check-cidr CIDR" exits 1, with the error, if
+	// this server would refuse CIDR in its TRUSTED_PROXIES.
+	// bin/entrypoint.sh runs it on each entry it gives nginx.
+	if len(os.Args) == 3 && os.Args[1] == "check-cidr" {
+		_, err := middleware.ParseTrustedProxies(os.Args[2:])
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+
+		return
+	}
+
+	// "netwatch-server prepare-data-dir DATA_DIR" gets DATA_DIR ready
+	// for the netwatch user, or exits 1 with the error; see
+	// reportbuf.PrepareDataDir. bin/entrypoint.sh runs it as root
+	// before it starts this server as that user.
+	if len(os.Args) == 3 && os.Args[1] == "prepare-data-dir" {
+		netwatch, err := user.Lookup("netwatch")
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+
+		err = reportbuf.PrepareDataDir("/data", os.Args[2], netwatch)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "DATA_DIR '%s': %v\n", os.Args[2], err)
+			os.Exit(1)
+		}
+
+		return
+	}
+
+	globals.Appname = Appname
+	globals.Version = Version
+
+	fx.New(
+		// fx logs each step of starting and stopping through the
+		// server's own logger, so off a terminal those lines are
+		// JSON like every other line.
+		fx.WithLogger(func(log *logger.Logger) fxevent.Logger {
+			return &fxevent.SlogLogger{Logger: log.Get()}
+		}),
+		fx.Provide(
+			config.New,
+			globals.New,
+			handlers.New,
+			healthcheck.New,
+			logger.New,
+			middleware.New,
+			reportbuf.New,
+			server.New,
+		),
+		fx.Invoke(
+			// First, so the name and version are logged even when
+			// a setting stops the start.
+			func(log *logger.Logger) { log.Identify() },
+			func(*server.Server) {},
+		),
+	).Run()
+}