Add DEBUG-gated panel to buy any card in the shop

When the server's DEBUG env var is on, expose a card catalog endpoint
and a collapsible client panel that drops any pet or food straight into
your deck (free, off-turn). Gated server-side so it is inert in normal
play.

cmd/server/main.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"strings"
 	"syscall"
 	"time"
 
@@ -17,6 +18,15 @@ import (
 	"github.com/greyson/super-auto-pets-board-game/internal/store"
 )
 
+// isTruthy reports whether an env value means "on".
+func isTruthy(v string) bool {
+	switch strings.ToLower(strings.TrimSpace(v)) {
+	case "1", "true", "yes", "on":
+		return true
+	}
+	return false
+}
+
 func main() {
 	if err := env.Load(".env"); err != nil {
 		slog.Error("failed to read .env", "err", err)
@@ -25,6 +35,10 @@ func main() {
 	dataDir := env.Get("DATA_DIR", "data")
 	port := env.Get("PORT", "8080")
 	staticDir := env.Get("STATIC_DIR", "web/dist")
+	debug := isTruthy(env.Get("DEBUG", ""))
+	if debug {
+		slog.Warn("DEBUG mode on: the buy-any-card panel is enabled")
+	}
 
 	st, err := store.Open(dataDir)
 	if err != nil {
@@ -40,7 +54,7 @@ func main() {
 
 	srv := &http.Server{
 		Addr:    ":" + port,
-		Handler: server.New(st, staticDir).Handler(),
+		Handler: server.New(st, staticDir, debug).Handler(),
 	}
 
 	go func() {