debug: add diagnostic logging for label suggestion flow

Log key points in /api/ai/tags and ContextualAutoTagService to trace
where label suggestions fail: notebook lookup, AI raw response,
JSON parsing, filtered results.

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

memento-note/app/api/ai/tags/route.ts

@@ -31,6 +31,7 @@ export async function POST(req: NextRequest) {
     // If notebookId is provided, use contextual suggestions (IA2)
     if (notebookId) {
       try {
+        console.log('[/api/ai/tags] contextual request — notebookId:', notebookId, 'content length:', content.length)
         const suggestions = await contextualAutoTagService.suggestLabels(
           content,
           notebookId,
@@ -38,6 +39,8 @@ export async function POST(req: NextRequest) {
           language
         );
 
+        console.log('[/api/ai/tags] suggestions:', suggestions.length, suggestions.map(s => `${s.label}(${s.confidence})`))
+
         const convertedTags = suggestions.map(s => ({
           tag: s.label,
           confidence: s.confidence,