fix(terminal): add collision detection for terminal drag and drop reordering (#985)

* fix(terminal): add collision detection for terminal drag and drop reordering

Add closestCenter collision detection to DndContext to fix terminal
drag and drop swapping not detecting valid drop targets. The default
rectIntersection algorithm required too much overlap for grid layouts.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix(terminal): handle file drops when closestCenter returns sortable ID

Address PR review feedback:
- Fix file drop handling to work when closestCenter collision detection
  returns the sortable ID instead of the droppable ID
- Add terminals to useCallback dependency array to prevent stale state

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

apps/frontend/src/renderer/components/TerminalGrid.tsx

@@ -12,7 +12,8 @@ import {
   PointerSensor,
   KeyboardSensor,
   useSensor,
-  useSensors
+  useSensors,
+  closestCenter,
 } from '@dnd-kit/core';
 import {
   SortableContext,
@@ -292,17 +293,22 @@ export function TerminalGrid({ projectPath, onNewTaskClick, isActive = false }:
 
     // Handle file drop on terminal
     const overId = over.id.toString();
-    if (overId.startsWith('terminal-')) {
-      const terminalId = overId.replace('terminal-', '');
+    let terminalId: string | null = null;
 
-      if (activeData?.path) {
-        // Quote the path if it contains spaces
-        const quotedPath = activeData.path.includes(' ') ? `"${activeData.path}"` : activeData.path;
-        // Insert the file path into the terminal with a trailing space
-        window.electronAPI.sendTerminalInput(terminalId, quotedPath + ' ');
-      }
+    if (overId.startsWith('terminal-')) {
+      terminalId = overId.replace('terminal-', '');
+    } else if (terminals.some(t => t.id === overId)) {
+      // closestCenter might return the sortable ID instead of droppable ID
+      terminalId = overId;
     }
-  }, [reorderTerminals]);
+
+    if (terminalId && activeData?.path) {
+      // Quote the path if it contains spaces
+      const quotedPath = activeData.path.includes(' ') ? `"${activeData.path}"` : activeData.path;
+      // Insert the file path into the terminal with a trailing space
+      window.electronAPI.sendTerminalInput(terminalId, quotedPath + ' ');
+    }
+  }, [reorderTerminals, terminals]);
 
   // Calculate grid layout based on number of terminals
   const gridLayout = useMemo(() => {
@@ -358,6 +364,7 @@ export function TerminalGrid({ projectPath, onNewTaskClick, isActive = false }:
   return (
     <DndContext
       sensors={sensors}
+      collisionDetection={closestCenter}
       onDragStart={handleDragStart}
       onDragEnd={handleDragEnd}
     >