feat(ST-1112): add Suspense skeleton for edit-mode task loading

Extracts task fetch into EditTaskLoader (async server component) so
the sprint board renders immediately while the task loads.
TaskDialogSkeleton shows 3 grey bars during the fetch. Invalid or
out-of-scope task IDs redirect to closePath.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/_components/tasks/edit-task-loader.tsx

@@ -0,0 +1,47 @@
+import { redirect } from 'next/navigation'
+import { prisma } from '@/lib/prisma'
+import { productAccessFilter } from '@/lib/product-access'
+import { TaskDialog } from './task-dialog'
+
+interface EditTaskLoaderProps {
+  taskId: string
+  userId: string
+  productId: string
+  closePath: string
+  isDemo: boolean
+}
+
+export async function EditTaskLoader({
+  taskId,
+  userId,
+  productId,
+  closePath,
+  isDemo,
+}: EditTaskLoaderProps) {
+  const task = await prisma.task.findFirst({
+    where: {
+      id: taskId,
+      story: { product: productAccessFilter(userId) },
+    },
+    select: {
+      id: true,
+      title: true,
+      description: true,
+      implementation_plan: true,
+      priority: true,
+      status: true,
+      created_at: true,
+    },
+  })
+
+  if (!task) redirect(closePath)
+
+  return (
+    <TaskDialog
+      task={task}
+      productId={productId}
+      closePath={closePath}
+      isDemo={isDemo}
+    />
+  )
+}