Fix Shift+arrow range selection: track anchor (fixed) and focus (moving) separately

Previous approach always started from the lowest-indexed selected entry, causing the range to snap to anchor on arrow reversal. Now arrowFocus tracks the moving end; arrowAnchor stays fixed. Non-Shift arrow resets both to the new position.

js/app.js

@@ -23,6 +23,7 @@ let showTrash = false;
 let selectedIds = new Set();
 let lastSelectedId = null;
 let arrowAnchor = -1;
+let arrowFocus = -1;
 let rectState = { active: false, startX: 0, startY: 0, el: null, started: false };
 
 // ==================== SOUND ====================
@@ -1083,6 +1084,7 @@ function toggleSelectEntry(id, e) {
     }
     lastSelectedId = id;
     arrowAnchor = -1;
+    arrowFocus = -1;
     updateBatchBar();
     render();
 }
@@ -1091,6 +1093,7 @@ function clearSelection() {
     selectedIds.clear();
     lastSelectedId = null;
     arrowAnchor = -1;
+    arrowFocus = -1;
     hideBatchBar();
     render();
 }
@@ -1426,8 +1429,8 @@ document.addEventListener('keydown', function(e) {
         const filtered = getFilteredEntries();
         if (!filtered.length) return;
         const isNext = e.key === 'ArrowDown' || e.key === 'ArrowRight';
-        let idx = -1;
-        if (selectedIds.size > 0) {
+        let idx = arrowFocus >= 0 ? arrowFocus : -1;
+        if (idx < 0 && selectedIds.size > 0) {
             const firstId = [...selectedIds][0];
             idx = filtered.findIndex(e => e.id == firstId);
         }
@@ -1440,13 +1443,15 @@ document.addEventListener('keydown', function(e) {
         }
         if (e.shiftKey) {
             if (arrowAnchor < 0) arrowAnchor = idx;
-            const start = Math.min(arrowAnchor, idx), end = Math.max(arrowAnchor, idx);
+            arrowFocus = idx;
+            const start = Math.min(arrowAnchor, arrowFocus), end = Math.max(arrowAnchor, arrowFocus);
             selectedIds.clear();
             for (let i = start; i <= end; i++) selectedIds.add(filtered[i].id);
         } else {
             selectedIds.clear();
             selectedIds.add(filtered[idx].id);
-            if (arrowAnchor < 0) arrowAnchor = idx;
+            arrowAnchor = idx;
+            arrowFocus = idx;
         }
         updateBatchBar(); render(); playSound('click');
         return;