feat(backlog): add EmptyPanel shared component, replace inline empty states

EmptyPanel takes title?, message, and optional action with DemoTooltip.
Replaces duplicate inline empty-state markup in pbi-list and story-panel.

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

components/backlog/empty-panel.tsx

@@ -0,0 +1,35 @@
+'use client'
+
+import { Button } from '@/components/ui/button'
+import { DemoTooltip } from '@/components/shared/demo-tooltip'
+
+interface EmptyPanelProps {
+  title?: string
+  message: string
+  action?: {
+    label: string
+    onClick: () => void
+    disabled?: boolean
+  }
+}
+
+export function EmptyPanel({ title, message, action }: EmptyPanelProps) {
+  return (
+    <div className="p-8 text-center text-muted-foreground space-y-3">
+      {title && <p className="text-sm font-medium text-foreground">{title}</p>}
+      <p className="text-sm">{message}</p>
+      {action && (
+        <DemoTooltip show={action.disabled ?? false}>
+          <Button
+            size="sm"
+            variant="outline"
+            disabled={action.disabled}
+            onClick={action.disabled ? undefined : action.onClick}
+          >
+            {action.label}
+          </Button>
+        </DemoTooltip>
+      )}
+    </div>
+  )
+}

components/backlog/pbi-list.tsx

@@ -32,6 +32,7 @@ import { reorderPbisAction, updatePbiPriorityAction } from '@/actions/stories'
 import { cn } from '@/lib/utils'
 import { PbiDialog, type PbiDialogState } from './pbi-dialog'
 import { BacklogCard } from './backlog-card'
+import { EmptyPanel } from './empty-panel'
 import { DemoTooltip } from '@/components/shared/demo-tooltip'
 import { PRIORITY_COLORS } from '@/components/shared/priority-select'
 import { PBI_STATUS_LABELS, PBI_STATUS_COLORS } from '@/components/shared/pbi-status-select'
@@ -417,14 +418,10 @@ export function PbiList({ productId, pbis, isDemo }: PbiListProps) {
 
       <div className="flex-1 overflow-y-auto">
         {pbis.length === 0 ? (
-          <div className="p-8 text-center text-muted-foreground text-sm space-y-3">
-            <p>Nog geen PBI&apos;s aangemaakt.</p>
-            <DemoTooltip show={isDemo}>
-              <Button size="sm" variant="outline" disabled={isDemo} onClick={() => !isDemo && setDialogState({ mode: 'create', productId, defaultPriority: 2 })}>
-                Maak je eerste PBI aan
-              </Button>
-            </DemoTooltip>
-          </div>
+          <EmptyPanel
+            message="Nog geen PBI's aangemaakt."
+            action={{ label: 'Maak je eerste PBI aan', onClick: () => setDialogState({ mode: 'create', productId, defaultPriority: 2 }), disabled: isDemo }}
+          />
         ) : (
           <DndContext
             id="pbi-list"

components/backlog/story-panel.tsx

@@ -30,6 +30,7 @@ import { usePlannerStore } from '@/stores/planner-store'
 import { reorderStoriesAction } from '@/actions/stories'
 import { StoryDialog, type StoryDialogState } from './story-dialog'
 import { BacklogCard } from './backlog-card'
+import { EmptyPanel } from './empty-panel'
 import { DemoTooltip } from '@/components/shared/demo-tooltip'
 import { cn } from '@/lib/utils'
 
@@ -242,20 +243,12 @@ export function StoryPanel({ productId, storiesByPbi, isDemo }: StoryPanelProps)
 
       <div className="flex-1 overflow-y-auto p-4">
         {selectedPbiId === null ? (
-          <p className="text-sm text-muted-foreground text-center mt-8">
-            Selecteer een PBI om de stories te bekijken.
-          </p>
+          <EmptyPanel message="Selecteer een PBI om de stories te bekijken." />
         ) : rawStories.length === 0 ? (
-          <div className="text-center mt-8 space-y-3">
-            <p className="text-sm text-muted-foreground">Nog geen stories voor dit PBI.</p>
-            {selectedPbiId && (
-              <DemoTooltip show={isDemo}>
-                <Button size="sm" variant="outline" disabled={isDemo} onClick={() => !isDemo && setStoryDialogState({ mode: 'create', pbiId: selectedPbiId, productId, defaultPriority: 2 })}>
-                  Maak je eerste story aan
-                </Button>
-              </DemoTooltip>
-            )}
-          </div>
+          <EmptyPanel
+            message="Nog geen stories voor dit PBI."
+            action={{ label: 'Maak je eerste story aan', onClick: () => setStoryDialogState({ mode: 'create', pbiId: selectedPbiId, productId, defaultPriority: 2 }), disabled: isDemo }}
+          />
         ) : (
           <DndContext
             id="story-panel"