perf(ui): use binary search for visible column window in VirtualResultGrid

lib/features/main_screen/result_grid_view.dart

@@ -125,16 +125,34 @@ ResultGridColumnWindow computeVisibleColumnWindow({
   final start = scrollOffset.clamp(0.0, total);
   final end = (scrollOffset + viewportWidth).clamp(0.0, total);
 
-  // First column with any pixel past [start].
+  // First column with any pixel past [start]: smallest index where columnOffsets[first + 1] > start
   var first = 0;
-  while (first < n && columnOffsets[first + 1] <= start) {
-    first++;
+  var low = 0;
+  var high = n - 1;
+  while (low <= high) {
+    final mid = (low + high) ~/ 2;
+    if (columnOffsets[mid + 1] > start) {
+      first = mid;
+      high = mid - 1;
+    } else {
+      low = mid + 1;
+    }
   }
-  // Last column with any pixel before [end].
+
+  // Last column with any pixel before [end]: largest index where columnOffsets[last] < end
   var last = n - 1;
-  while (last > 0 && columnOffsets[last] >= end) {
-    last--;
+  low = 0;
+  high = n - 1;
+  while (low <= high) {
+    final mid = (low + high) ~/ 2;
+    if (columnOffsets[mid] < end) {
+      last = mid;
+      low = mid + 1;
+    } else {
+      high = mid - 1;
+    }
   }
+
   if (first > last) {
     first = last.clamp(0, n - 1);
   }

test/features/main_screen/results_tab_test.dart

@@ -106,6 +106,24 @@ void main() {
       expect(window.last, lessThan(30));
       expect(window.leadingWidth, greaterThan(0));
     });
+
+    test('handles large scale column sets (10000 columns) efficiently', () {
+      final widths = List<double>.filled(10000, 100);
+      final offsets = computeResultGridColumnOffsets(widths);
+      final window = computeVisibleColumnWindow(
+        columnWidths: widths,
+        columnOffsets: offsets,
+        scrollOffset: 500000,
+        viewportWidth: 1000,
+        overscanColumns: 2,
+      );
+      // scrollOffset 500000 = index 5000 (since width is 100)
+      // viewport 1000 = 10 columns (indices 5000..5009)
+      // with overscan 2 -> first: 4998, last: 5011
+      expect(window.first, 4998);
+      expect(window.last, 5011);
+      expect(window.leadingWidth, 4998 * 100.0);
+    });
   });
 
   group('ResultsTab', () {