feat: smart note history with manual/auto modes, delete entries, i18n fixes

- Add noteHistoryMode setting (manual default / auto) with DB migration
- Manual mode: commit button in editor toolbar creates snapshots on demand
- Auto mode: smart snapshots with 20-char diff threshold + 5min cooldown,
  structural changes (color, pin, archive, labels) bypass cooldown
- Add delete individual history entries from history modal
- Fix sidebar: Notes nav no longer active on notebook pages
- Fix sidebar icon: replace filled Lightbulb with outlined FileText
- Fix title suggestions: change from amber to sky blue color scheme
- Fix hydration mismatch: add suppressHydrationWarning on locale dates
- Complete i18n: add history, sort, and AI chat translations for all 16 languages
- Translate French AI assistant section (40+ keys) from English to French
- Update README with new features and stack info

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

memento-note/prisma/schema.prisma

@@ -30,6 +30,7 @@ model User {
   labels             Label[]
   memoryEchoInsights MemoryEchoInsight[]
   notes              Note[]
+  noteHistories      NoteHistory[]
   sentShares         NoteShare[]         @relation("SentShares")
   receivedShares     NoteShare[]         @relation("ReceivedShares")
   notebooks          Notebook[]
@@ -152,6 +153,7 @@ model Note {
   noteEmbedding       NoteEmbedding?
   shares              NoteShare[]
   labelRelations      Label[]             @relation("LabelToNote")
+  historyEntries      NoteHistory[]
 
   @@index([isPinned])
   @@index([isArchived])
@@ -162,6 +164,34 @@ model Note {
   @@index([userId, notebookId])
 }
 
+model NoteHistory {
+  id         String   @id @default(cuid())
+  noteId      String
+  userId      String
+  version     Int
+  reason      String?
+  title       String?
+  content     String
+  color       String
+  isPinned    Boolean
+  isArchived  Boolean
+  type        String
+  checkItems  String?
+  labels      String?
+  images      String?
+  links       String?
+  isMarkdown  Boolean
+  size        String
+  notebookId  String?
+  createdAt   DateTime @default(now())
+  note        Note     @relation(fields: [noteId], references: [id], onDelete: Cascade)
+  user        User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([noteId, version])
+  @@index([noteId, createdAt(sort: Desc)])
+  @@index([userId, noteId, createdAt(sort: Desc)])
+}
+
 model NoteShare {
   id          String    @id @default(cuid())
   noteId      String
@@ -244,6 +274,8 @@ model UserAISettings {
   desktopNotifications Boolean @default(false)
   anonymousAnalytics   Boolean @default(false)
   autoLabeling         Boolean @default(true)
+  noteHistory          Boolean @default(false)
+  noteHistoryMode      String  @default("manual")
   languageDetection    Boolean @default(true)
   user                 User    @relation(fields: [userId], references: [id], onDelete: Cascade)