fix: label system overhaul - sync dual storage, fix suggestions

- Replace broken upsert (nbScope ?? '') with findFirst+create for null notebookId
- Remove aggressive orphan cleanup that deleted notebook labels after save
- Add syncNoteLabels() to update both Note.labels JSON and labelRelations
- Fix createNote, updateNote, auto-labeling to use syncNoteLabels
- Add fallback: suggestFromExistingLabels → suggestNewLabels if empty
- Lower confidence threshold 0.6→0.3, max suggestions 3→5
- Case-insensitive label matching in suggestions

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

memento-note/lib/ai/services/contextual-auto-tag.service.ts

@@ -55,10 +55,12 @@ export class ContextualAutoTagService {
 
     // CASE 1: Notebook has existing labels → suggest from them (IA2)
     if (notebook.labels.length > 0) {
-      return await this.suggestFromExistingLabels(noteContent, notebook, language)
+      const existing = await this.suggestFromExistingLabels(noteContent, notebook, language)
+      if (existing.length > 0) return existing
+      // Fallback: no existing label matched → suggest new ones too
     }
 
-    // CASE 2: Notebook has NO labels → suggest NEW labels to create
+    // CASE 2: No labels in notebook (or none matched) → suggest NEW labels
     return await this.suggestNewLabels(noteContent, notebook, language)
   }
 
@@ -126,20 +128,23 @@ export class ContextualAutoTagService {
         return []
       }
 
-      // Filter and map suggestions
+      // Filter and map suggestions (case-insensitive)
+      const lowerAvailable = availableLabels.map((l: string) => l.toLowerCase())
       const suggestions = suggestionsArray
         .filter((s: any) => {
-          // Must be in available labels
-          return availableLabels.includes(s.label) && s.confidence > 0.6
+          return s.label && lowerAvailable.includes(s.label.toLowerCase()) && (s.confidence || 0) > 0.3
         })
-        .map((s: any) => ({
-          label: s.label,
+        .map((s: any) => {
+          const originalLabel = availableLabels.find((l: string) => l.toLowerCase() === s.label.toLowerCase()) || s.label
+          return {
+            label: originalLabel,
           confidence: Math.round(s.confidence * 100),
           reasoning: s.reasoning || '',
           isNewLabel: false,
-        }))
+          }
+        })
         .sort((a: any, b: any) => b.confidence - a.confidence)
-        .slice(0, 3) // Max 3 suggestions
+        .slice(0, 5)
 
       return suggestions as LabelSuggestion[]
     } catch (error) {
@@ -213,7 +218,7 @@ export class ContextualAutoTagService {
       // Filter and map suggestions
       const suggestions = suggestionsArray
         .filter((s: any) => {
-          return s.label && s.label.length > 0 && s.confidence > 0.6
+          return s.label && s.label.length > 0 && (s.confidence || 0) > 0.3
         })
         .map((s: any) => ({
           label: s.label,
@@ -222,7 +227,7 @@ export class ContextualAutoTagService {
           isNewLabel: true, // Mark as new label suggestion
         }))
         .sort((a: any, b: any) => b.confidence - a.confidence)
-        .slice(0, 3) // Max 3 suggestions
+        .slice(0, 5)
 
       return suggestions as LabelSuggestion[]
     } catch (error) {