feat(01-03): cmd/worker Phase 1 skeleton (D-03)

- Opens pgxpool from DATABASE_URL, logs 'worker ready', blocks on
  SIGINT/SIGTERM, closes pool, exits 0
- Reuses web.NewSlogHandler — pure helper, no HTTP coupling
- No job queue libraries (river/asynq/pg_notify) — Phase 6 replaces this
  file in full
- 48 lines (under 80-line budget signals 'we did not implement Phase 6
  by accident')

backend/cmd/worker/main.go

@@ -0,0 +1,48 @@
+// Command worker is the Phase 1 worker skeleton (CONTEXT D-03). It boots,
+// opens a pgxpool, logs "worker ready", and blocks on SIGINT/SIGTERM until
+// shutdown. Phase 6 replaces this file with the real job runtime — keep it
+// minimal until then.
+package main
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"backend/internal/db"
+	"backend/internal/web"
+)
+
+func main() {
+	env := os.Getenv("ENV")
+	if env == "" {
+		env = "development"
+	}
+	dsn := os.Getenv("DATABASE_URL")
+
+	slog.SetDefault(slog.New(web.NewSlogHandler(env, os.Stdout)))
+
+	if dsn == "" {
+		slog.Error("DATABASE_URL is required but unset")
+		os.Exit(1)
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	pool, err := db.NewPool(ctx, dsn)
+	if err != nil {
+		slog.Error("db connect failed", "err", err)
+		os.Exit(1)
+	}
+
+	// Load-bearing signal per D-03 — verification scripts grep for this.
+	slog.Info("worker ready")
+
+	<-ctx.Done()
+	slog.Info("shutting down")
+	pool.Close()
+	slog.Info("shutdown complete")
+}