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- Fix sidebar: Notes nav no longer active on notebook pages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/app/api/notes/[id]/route.ts

@@ -2,6 +2,13 @@ import { NextRequest, NextResponse } from 'next/server'
 import prisma from '@/lib/prisma'
 import { auth } from '@/auth'
 import { parseNote } from '@/lib/utils'
+import {
+  createNoteHistorySnapshot,
+  getNoteHistoryMode,
+  isNoteHistoryEnabledForUser,
+  shouldCaptureHistorySnapshot,
+  shouldCreateAutoSnapshot,
+} from '@/lib/note-history'
 
 // GET /api/notes/[id] - Get a single note
 export async function GET(
@@ -134,6 +141,32 @@ export async function PUT(
       data: updateData,
     })
 
+    try {
+      const historyEnabled = await isNoteHistoryEnabledForUser(session.user.id)
+      if (historyEnabled && shouldCaptureHistorySnapshot(updateData)) {
+        const mode = await getNoteHistoryMode(session.user.id)
+        if (mode === 'auto') {
+          const shouldAuto = await shouldCreateAutoSnapshot({
+            noteId: id,
+            userId: session.user.id,
+            updateData,
+            existingContent: existingNote.content ?? '',
+            existingTitle: existingNote.title ?? null,
+          })
+          if (shouldAuto) {
+            await createNoteHistorySnapshot({
+              noteId: id,
+              userId: session.user.id,
+              reason: 'api:update',
+            })
+          }
+        }
+        // manual mode: no auto-snapshot
+      }
+    } catch (snapshotError) {
+      console.error('[HISTORY] Failed to create snapshot from /api/notes/[id] PUT:', snapshotError)
+    }
+
     return NextResponse.json({
       success: true,
       data: parseNote(note)