feat: Memento avec dates, Markdown, reminders et auth

Tests Playwright validés ✅:
- Création de notes: OK
- Modification titre: OK
- Modification contenu: OK
- Markdown éditable avec preview: OK

Fonctionnalités:
- date-fns: dates relatives sur cards
- react-markdown + remark-gfm
- Markdown avec toggle edit/preview
- Recherche améliorée (titre/contenu/labels/checkItems)
- Reminder recurrence/location (schema)
- NextAuth.js + User/Account/Session
- userId dans Note (optionnel)
- 4 migrations créées

Ready for production + auth integration

keep-notes/prisma/migrations/20260104144627_add_markdown/migration.sql

@@ -0,0 +1,29 @@
+-- RedefineTables
+PRAGMA defer_foreign_keys=ON;
+PRAGMA foreign_keys=OFF;
+CREATE TABLE "new_Note" (
+    "id" TEXT NOT NULL PRIMARY KEY,
+    "title" TEXT,
+    "content" TEXT NOT NULL,
+    "color" TEXT NOT NULL DEFAULT 'default',
+    "isPinned" BOOLEAN NOT NULL DEFAULT false,
+    "isArchived" BOOLEAN NOT NULL DEFAULT false,
+    "type" TEXT NOT NULL DEFAULT 'text',
+    "checkItems" TEXT,
+    "labels" TEXT,
+    "images" TEXT,
+    "reminder" DATETIME,
+    "isMarkdown" BOOLEAN NOT NULL DEFAULT false,
+    "order" INTEGER NOT NULL DEFAULT 0,
+    "createdAt" DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" DATETIME NOT NULL
+);
+INSERT INTO "new_Note" ("checkItems", "color", "content", "createdAt", "id", "images", "isArchived", "isPinned", "labels", "order", "reminder", "title", "type", "updatedAt") SELECT "checkItems", "color", "content", "createdAt", "id", "images", "isArchived", "isPinned", "labels", "order", "reminder", "title", "type", "updatedAt" FROM "Note";
+DROP TABLE "Note";
+ALTER TABLE "new_Note" RENAME TO "Note";
+CREATE INDEX "Note_isPinned_idx" ON "Note"("isPinned");
+CREATE INDEX "Note_isArchived_idx" ON "Note"("isArchived");
+CREATE INDEX "Note_order_idx" ON "Note"("order");
+CREATE INDEX "Note_reminder_idx" ON "Note"("reminder");
+PRAGMA foreign_keys=ON;
+PRAGMA defer_foreign_keys=OFF;