fix: Add debounced Undo/Redo system to avoid character-by-character history

- Add debounced state updates for title and content (500ms delay)
- Immediate UI updates with delayed history saving
- Prevent one-letter-per-undo issue
- Add cleanup for debounce timers on unmount

keep-notes/prisma/migrations/20260104094125_init/migration.sql

@@ -0,0 +1,20 @@
+-- CreateTable
+CREATE TABLE "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" JSONB,
+    "labels" JSONB,
+    "createdAt" DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" DATETIME NOT NULL
+);
+
+-- CreateIndex
+CREATE INDEX "Note_isPinned_idx" ON "Note"("isPinned");
+
+-- CreateIndex
+CREATE INDEX "Note_isArchived_idx" ON "Note"("isArchived");