feat(web,server): embed статики SPA + fallback, монтирование в cmd/server

internal/web/web.go

@@ -0,0 +1,43 @@
+// Package web embeds the built React SPA (web/dist, copied to
+// internal/web/dist by `make web` before go build/test) and serves it
+// with SPA-fallback: any non-file path resolves to index.html so
+// client-side routing works.
+package web
+
+import (
+	"embed"
+	"io/fs"
+	"net/http"
+	"strings"
+)
+
+//go:embed all:dist
+var distFS embed.FS
+
+// Handler serves the embedded SPA with fallback to index.html for
+// client-side routes (any non-file path that isn't an API route).
+func Handler() (http.Handler, error) {
+	sub, err := fs.Sub(distFS, "dist")
+	if err != nil {
+		return nil, err
+	}
+	fileServer := http.FileServer(http.FS(sub))
+	index, err := fs.ReadFile(sub, "index.html")
+	if err != nil {
+		return nil, err
+	}
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// существующий файл (ассет) — отдать как есть
+		p := strings.TrimPrefix(r.URL.Path, "/")
+		if p != "" {
+			if f, err := sub.Open(p); err == nil {
+				_ = f.Close()
+				fileServer.ServeHTTP(w, r)
+				return
+			}
+		}
+		// иначе — SPA index
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		_, _ = w.Write(index)
+	}), nil
+}