UI Stabilization: Global color theme updates (#75B2D6), AI Assistant styling refactor, and navigation fixes

memento-note/prisma/schema.prisma

@@ -100,6 +100,7 @@ model Label {
   id         String    @id @default(cuid())
   name       String
   color      String    @default("gray")
+  type       String    @default("user")  // "ai" or "user"
   notebookId String?
   userId     String?
   createdAt  DateTime  @default(now())
@@ -282,6 +283,7 @@ model UserAISettings {
   noteHistoryMode      String  @default("manual")
   languageDetection    Boolean @default(true)
   fontFamily           String  @default("inter")
+  autoSave             Boolean @default(true)
   user                 User    @relation(fields: [userId], references: [id], onDelete: Cascade)
 
   @@index([memoryEcho])