fix: KB Accelerator tree builder, approve all, canvas delete button

- Fix _build_troubleshooting_tree() to handle deep nesting, warning nodes,
  and DAG deduplication (placed set prevents duplicate IDs)
- Fix step_sync VARCHAR(255) overflow on publish by truncating title
- Add "Approve All" button to KB review screen
- Add delete button (hover-reveal) to flow canvas nodes

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

frontend/src/pages/KBAcceleratorPage.tsx

@@ -89,6 +89,26 @@ export default function KBAcceleratorPage() {
     }
   }
 
+  const handleApproveAll = async () => {
+    if (!importId || !kbImport) return
+    const unapproved = kbImport.nodes.filter(n => !n.user_approved)
+    if (unapproved.length === 0) return
+    setLoading(true)
+    try {
+      await Promise.all(
+        unapproved.map(n => kbAcceleratorApi.editNode(importId, n.id, { operation: 'approve' }))
+      )
+      setKbImport(prev => {
+        if (!prev) return prev
+        return { ...prev, nodes: prev.nodes.map(n => ({ ...n, user_approved: true })) }
+      })
+    } catch {
+      toast.error('Failed to approve all nodes')
+    } finally {
+      setLoading(false)
+    }
+  }
+
   const handleEditNode = async (nodeId: string, data: KBNodeEditRequest) => {
     if (!importId) return
     const updatedNode = await kbAcceleratorApi.editNode(importId, nodeId, data)
@@ -149,9 +169,9 @@ export default function KBAcceleratorPage() {
   }
 
   return (
-    <div className="flex flex-col h-full p-6">
+    <div className="flex flex-col h-full min-h-0 p-6">
       {/* Page title */}
-      <div className="flex items-center gap-3 mb-6">
+      <div className="shrink-0 flex items-center gap-3 mb-6">
         <Sparkles size={24} className="text-primary" />
         <h1 className="text-2xl font-heading font-bold text-foreground">KB Accelerator</h1>
       </div>
@@ -181,13 +201,16 @@ export default function KBAcceleratorPage() {
       )}
 
       {phase === 'review' && kbImport && (
-        <ReviewScreen
-          kbImport={kbImport}
-          onEditNode={handleEditNode}
-          onCommit={handleCommit}
-          onDiscard={handleDiscard}
-          loading={loading}
-        />
+        <div className="flex-1 min-h-0">
+          <ReviewScreen
+            kbImport={kbImport}
+            onEditNode={handleEditNode}
+            onApproveAll={handleApproveAll}
+            onCommit={handleCommit}
+            onDiscard={handleDiscard}
+            loading={loading}
+          />
+        </div>
       )}
 
       {phase === 'success' && commitResult && (

frontend/src/pages/TreeEditorPage.tsx

@@ -815,6 +815,7 @@ export function TreeEditorPage() {
           editingNodeId={editorAI.isOpen ? null : editingNodeId}
           onNodeSelect={handleNodeSelect}
           onSelectAnswerType={handleSelectAnswerType}
+          onNodeDelete={deleteNode}
           onNodeContextMenu={editorAI.openContextMenu}
         />
       </div>