feat: Replace alert() with professional toast notification system

- Remove buggy Undo/Redo that saved character-by-character
- Simplify state to plain useState like Google Keep
- Create toast component with success/error/warning/info types
- Toast notifications auto-dismiss after 3s with smooth animations
- Add ToastProvider in layout
- Remove all JavaScript alert() calls
- Production-ready notification system

mcp_workflow.json

@@ -0,0 +1,91 @@
+{
+  "meta": {
+    "instanceId": "memento-demo"
+  },
+  "nodes": [
+    {
+      "parameters": {},
+      "id": "b1c9e8f2-1234-4567-89ab-cdef12345678",
+      "name": "Déclencheur Manuel (Start)",
+      "type": "n8n-nodes-base.manualTrigger",
+      "typeVersion": 1,
+      "position": [
+        250,
+        300
+      ]
+    },
+    {
+      "parameters": {
+        "values": {
+          "string": [
+            {
+              "name": "subject",
+              "value": "Réunion Projet MCP"
+            },
+            {
+              "name": "body",
+              "value": "N'oublie pas de vérifier l'intégration N8N aujourd'hui à 15h00."
+            },
+            {
+              "name": "labels",
+              "value": "['work', 'n8n']"
+            }
+          ]
+        },
+        "options": {}
+      },
+      "id": "a2b3c4d5-1234-4567-89ab-cdef12345678",
+      "name": "Simuler Email (Données)",
+      "type": "n8n-nodes-base.set",
+      "typeVersion": 3.3,
+      "position": [
+        500,
+        300
+      ]
+    },
+    {
+      "parameters": {
+        "prompt": "Tu es un assistant personnel. Utilise l'outil MCP 'memento' pour créer une nouvelle note.\n\nDétails de la note :\n- Titre : {{ $json.subject }}\n- Contenu : {{ $json.body }}\n- Labels : {{ $json.labels }}\n\nIMPORTANT : Utilise l'outil create_note disponible dans le serveur MCP.",
+        "options": {}
+      },
+      "id": "e4f5g6h7-1234-4567-89ab-cdef12345678",
+      "name": "AI Agent (MCP Client)",
+      "type": "@n8n/n8n-nodes-langchain.agent",
+      "typeVersion": 1.5,
+      "position": [
+        750,
+        300
+      ],
+      "credentials": {
+        "openAiApi": {
+          "id": "1",
+          "name": "OpenAI (N'oubliez pas de configurer votre clé)"
+        }
+      }
+    }
+  ],
+  "connections": {
+    "Déclencheur Manuel (Start)": {
+      "main": [
+        [
+          {
+            "node": "Simuler Email (Données)",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    },
+    "Simuler Email (Données)": {
+      "main": [
+        [
+          {
+            "node": "AI Agent (MCP Client)",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    }
+  }
+}