fix: auto-tagging provider resolution, email test flow, language detection

Auto-tagging:
- CRITICAL FIX: contextual-auto-tag.service.ts was calling getAIProvider()
  (alias for getEmbeddingsProvider) instead of getTagsProvider(). This meant
  auto-tagging used the embeddings provider/model instead of the tags one.
  Now correctly uses getTagsProvider() in both suggestFromExistingLabels and
  suggestNewLabels methods.
- Pass user's detected language to suggestLabels() for localized prompts
  (was hardcoded to 'en')

Email:
- Fix Resend "from" field: pass DB config to sendViaResend() instead of
  re-fetching from DB. Uses SMTP_FROM from config, with localhost-aware fallback.
- Add "Sender email" field in admin Resend section so users can set SMTP_FROM
- Save SMTP_FROM when Resend is selected (was only saved for SMTP mode)
- Test email button now saves config to DB BEFORE testing, so unsaved form
  values are used (was reading stale DB values)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

memento-note/app/actions/notes.ts

@@ -509,10 +509,26 @@ export async function createNote(data: {
           console.log('[BG] Auto-labeling check: enabled=', autoLabelingEnabled, 'confidence=', autoLabelingConfidence, 'notebookId=', notebookId)
 
           if (autoLabelingEnabled) {
+            // Detect user's language from their existing notes for localized prompts
+            let userLang = 'en'
+            try {
+              const langResult = await prisma.note.groupBy({
+                by: ['language'],
+                where: { userId, language: { not: null } },
+                _count: true,
+                orderBy: { _count: { language: 'desc' } },
+                take: 1,
+              })
+              if (langResult.length > 0 && langResult[0].language) {
+                userLang = langResult[0].language
+              }
+            } catch {}
+
             const suggestions = await contextualAutoTagService.suggestLabels(
               content,
               notebookId,
-              userId
+              userId,
+              userLang
             )
 
             console.log('[BG] Auto-labeling suggestions:', suggestions.length, suggestions.map(s => s.label))