blocked dates page and warning for special-cake orders

Add blocked_date table (migration 5), model, and store CRUD methods.
Add management page at /blocked with add/delete functionality.
Add nav link 'Terminy zablokowane' with event_busy icon.
Pass blocked dates to order form as JSON data attribute.
On form submit, if the order has special cakes and the date is
blocked, show a confirm() dialog warning the user.

server/post.go

@@ -142,6 +142,29 @@ func safeStr(s []string, i int) string {
 	return ""
 }
 
+func (h *Server) postBlocked(r *http.Request) (templ.Component, int, error) {
+	if err := r.ParseForm(); err != nil {
+		return nil, http.StatusBadRequest, err
+	}
+	if err := h.s.AddBlockedDate(r.FormValue("date")); err != nil {
+		return nil, http.StatusInternalServerError, err
+	}
+	dates, _ := h.s.GetBlockedDates()
+	return templates.BlockedMain(dates), http.StatusOK, nil
+}
+
+func (h *Server) deleteBlocked(r *http.Request) (templ.Component, int, error) {
+	id, err := strconv.Atoi(r.PathValue("id"))
+	if err != nil {
+		return nil, http.StatusBadRequest, err
+	}
+	if err := h.s.RemoveBlockedDate(id); err != nil {
+		return nil, http.StatusInternalServerError, err
+	}
+	dates, _ := h.s.GetBlockedDates()
+	return templates.BlockedMain(dates), http.StatusOK, nil
+}
+
 func (h *Server) updateStatus(r *http.Request) (templ.Component, int, error) {
 	id, err := strconv.Atoi(r.PathValue("id"))
 	if err != nil {