Replace Resend with n8n webhook relay for emails

- email.ts: POST to N8N_EMAIL_WEBHOOK_URL instead of Resend API
- env.ts: replace RESEND_API_KEY with N8N_EMAIL_WEBHOOK_URL
- .env.example: document new env var
- Add n8n workflow JSON (Webhook -> Gmail -> Respond) ready to import

n8n-workflows/naturcalabacera-email-relay.json

@@ -0,0 +1,71 @@
+{
+  "name": "Naturcalabacera - Email Relay",
+  "nodes": [
+    {
+      "parameters": {
+        "httpMethod": "POST",
+        "path": "naturcalabacera-email",
+        "responseMode": "responseNode",
+        "options": {}
+      },
+      "id": "webhook-naturcalabacera",
+      "name": "Webhook (POST email)",
+      "type": "n8n-nodes-base.webhook",
+      "typeVersion": 2,
+      "position": [240, 300]
+    },
+    {
+      "parameters": {
+        "sendTo": "={{ $json.body.to }}",
+        "subject": "={{ $json.body.subject }}",
+        "emailType": "html",
+        "message": "={{ $json.body.html }}",
+        "options": {}
+      },
+      "id": "gmail-send",
+      "name": "Gmail — Enviar",
+      "type": "n8n-nodes-base.gmail",
+      "typeVersion": 2.1,
+      "position": [520, 300]
+    },
+    {
+      "parameters": {
+        "respondWith": "json",
+        "responseBody": "={{ { success: true, id: $json.id } }}",
+        "options": {}
+      },
+      "id": "respond-ok",
+      "name": "Responder OK",
+      "type": "n8n-nodes-base.respondToWebhook",
+      "typeVersion": 1.1,
+      "position": [800, 300]
+    }
+  ],
+  "connections": {
+    "Webhook (POST email)": {
+      "main": [
+        [
+          {
+            "node": "Gmail — Enviar",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    },
+    "Gmail — Enviar": {
+      "main": [
+        [
+          {
+            "node": "Responder OK",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    }
+  },
+  "settings": {
+    "executionOrder": "v1"
+  }
+}