fix: label management - transaction safety, deletion sync, error handling

- Use prisma.$transaction in auto-label-creation.service with tx client
- Fix DELETE /api/labels to properly JSON.parse + disconnect labelRelations
- Fix PUT /api/labels rename to handle JSON labels
- Graceful error handling in /api/ai/tags and /api/ai/auto-labels
- Client-side label-deleted event in home-client, notes-tabs-view, label-management-dialog

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/app/api/labels/[id]/route.ts

@@ -114,7 +114,10 @@ export async function PUT(
       for (const note of allNotes) {
         if (note.labels) {
           try {
-            const noteLabels: string[] = Array.isArray(note.labels) ? (note.labels as string[]) : []
+            const parsed = typeof note.labels === 'string' ? JSON.parse(note.labels) : note.labels
+            const noteLabels: string[] = Array.isArray(parsed)
+              ? parsed.filter((n): n is string => typeof n === 'string')
+              : []
             const updatedLabels = noteLabels.map(l =>
               l.toLowerCase() === currentLabel.name.toLowerCase() ? newName : l
             )
@@ -123,8 +126,8 @@ export async function PUT(
               await prisma.note.update({
                 where: { id: note.id },
                 data: {
-                  labels: updatedLabels as any
-                }
+                  labels: updatedLabels.length > 0 ? JSON.stringify(updatedLabels) : null,
+                },
               })
             }
           } catch (e) {
@@ -197,36 +200,50 @@ export async function DELETE(
       return NextResponse.json({ error: 'Forbidden' }, { status: 403 })
     }
 
-    // For backward compatibility, remove from old label field in notes
+    // Remove label from all notes that have it (JSON + labelRelations)
     const targetUserIdDel = label.userId || label.notebook?.userId || session.user.id;
     if (targetUserIdDel) {
       const allNotes = await prisma.note.findMany({
         where: {
           userId: targetUserIdDel,
-          labels: { not: null }
+          OR: [
+            { labels: { not: null } },
+            { labelRelations: { some: { id: label.id } } },
+          ],
         },
         select: { id: true, labels: true }
       })
 
       for (const note of allNotes) {
+        let noteLabels: string[] = []
         if (note.labels) {
           try {
-            const noteLabels: string[] = Array.isArray(note.labels) ? (note.labels as string[]) : []
-            const filteredLabels = noteLabels.filter(
-              l => l.toLowerCase() !== label.name.toLowerCase()
-            )
-
-            if (filteredLabels.length !== noteLabels.length) {
-              await prisma.note.update({
-                where: { id: note.id },
-                data: {
-                  labels: (filteredLabels.length > 0 ? filteredLabels : null) as any
-                }
-              })
-            }
-          } catch (e) {
+            const parsed = typeof note.labels === 'string' ? JSON.parse(note.labels) : note.labels
+            noteLabels = Array.isArray(parsed)
+              ? parsed.filter((n): n is string => typeof n === 'string')
+              : []
+          } catch {
+            noteLabels = []
           }
         }
+
+        const filteredLabels = noteLabels.filter(
+          l => l.toLowerCase() !== label.name.toLowerCase()
+        )
+
+        const labelChanged = filteredLabels.length !== noteLabels.length
+
+        if (labelChanged) {
+          await prisma.note.update({
+            where: { id: note.id },
+            data: {
+              labels: filteredLabels.length > 0 ? JSON.stringify(filteredLabels) : null,
+              labelRelations: {
+                disconnect: { id: label.id },
+              },
+            },
+          })
+        }
       }
     }