⚡ performance optimization: batch fetch availableDates

Removed the 100ms artificial delay in `loadMenuDataFromAPI` and switched from sequentially awaiting fetch requests to concurrently awaiting requests in batches of 5 using `Promise.all`. Preserved original chronological ordering of array elements.

Co-authored-by: TauNeutrino <1600410+TauNeutrino@users.noreply.github.com>

benchmark_loadMenuDataFromAPI_concurrent.js

@@ -0,0 +1,26 @@
+const fs = require('fs');
+
+async function benchmark() {
+    let availableDates = Array.from({length: 30}).map((_, i) => ({ date: `2024-01-${i+1}`}));
+    const totalDates = availableDates.length;
+    let completed = 0;
+
+    console.log(`Starting benchmark for ${totalDates} items (Concurrent batch=5 without 100ms artificial delay)`);
+    const start = Date.now();
+
+    // Simulate Promise.all batching approach
+    const BATCH_SIZE = 5;
+    for (let i = 0; i < totalDates; i += BATCH_SIZE) {
+        const batch = availableDates.slice(i, i + BATCH_SIZE);
+        await Promise.all(batch.map(async (dateObj) => {
+            // mock fetch
+            await new Promise(r => setTimeout(r, 50)); // simulate network delay
+            completed++;
+        }));
+    }
+
+    const end = Date.now();
+    console.log(`Concurrent loading took ${end - start}ms`);
+}
+
+benchmark();