feat: Tage als geschlossen markierbar (Feiertage o. Ä.)

Im Wochenplan lässt sich pro Tag ein optionaler, mehrsprachiger
Schließungsgrund hinterlegen. Geschlossene Tage werden auf der
öffentlichen Speisekarte (Desktop + mobil) und im RSS-Feed als
"Geschlossen" statt mit Essenszeiten angezeigt, im Wochenplan bleibt
"Mahlzeit hinzufügen" für diesen Tag deaktiviert.

app/feed.xml/route.ts

@@ -1,5 +1,6 @@
 import { query } from "@/lib/db";
 import { loadMenuEntries } from "@/lib/db/menu-entries";
+import { listClosedDays } from "@/lib/db/closed-days";
 import { addDays, entriesFor, formatPrice, mondayOf, todayISO } from "@/lib/menu";
 import { localized, SITE_TITLE } from "@/lib/types";
 import type { Section } from "@/lib/types";
@@ -45,30 +46,38 @@ export async function GET() {
   // Wochennavigation anzeigt.
   const rangeEnd = addDays(monday, 11);
 
-  const [sections, entries] = await Promise.all([
+  const [sections, entries, closedDays] = await Promise.all([
     query<Section>("select * from sections order by sort"),
     loadMenuEntries(monday, rangeEnd),
+    listClosedDays(monday, rangeEnd),
   ]);
 
-  const days = Array.from(new Set(entries.map((e) => e.menu_date))).sort();
+  const days = Array.from(
+    new Set([...entries.map((e) => e.menu_date), ...closedDays.map((c) => c.closed_date)])
+  ).sort();
 
   const items = days
     .map((iso) => {
-      const dayContent = sections
-        .map((s) => {
-          const dishes = entriesFor(entries, iso, s.key);
-          if (dishes.length === 0) return "";
-          const list = dishes
-            .map(
-              (e) =>
-                `<li>${escapeXml(localized(e.dish, "de"))} – ${formatPrice(e.dish.price)}</li>`
-            )
+      const closed = closedDays.find((c) => c.closed_date === iso);
+      const dayContent = closed
+        ? `<p><strong>Geschlossen</strong>${
+            closed.reason ? ` – ${escapeXml(closed.reason)}` : ""
+          }</p>`
+        : sections
+            .map((s) => {
+              const dishes = entriesFor(entries, iso, s.key);
+              if (dishes.length === 0) return "";
+              const list = dishes
+                .map(
+                  (e) =>
+                    `<li>${escapeXml(localized(e.dish, "de"))} – ${formatPrice(e.dish.price)}</li>`
+                )
+                .join("");
+              return `<p><strong>${escapeXml(localized(s, "de"))} (${escapeXml(
+                s.time_range
+              )})</strong></p><ul>${list}</ul>`;
+            })
             .join("");
-          return `<p><strong>${escapeXml(localized(s, "de"))} (${escapeXml(
-            s.time_range
-          )})</strong></p><ul>${list}</ul>`;
-        })
-        .join("");
       if (!dayContent) return "";
 
       const [y, m, d] = iso.split("-").map(Number);