BE: API in-app messaging endpoint

Signed-off-by: jokob-sk <jokob.sk@gmail.com>

docs/API.md

@@ -59,6 +59,8 @@ http://<server>:<GRAPHQL_PORT>/
 * [Events](API_EVENTS.md) – Device event logging and management
 * [Sessions](API_SESSIONS.md) – Connection sessions and history
 * [Settings](API_SETTINGS.md) – Settings
+* Messaging:
+  * [In app messaging](API_MESSAGING_IN_APP.md) - In-app messaging
 * [Metrics](API_METRICS.md) – Prometheus metrics and per-device status
 * [Network Tools](API_NETTOOLS.md) – Utilities like Wake-on-LAN, traceroute, nslookup, nmap, and internet info
 * [Online History](API_ONLINEHISTORY.md) – Online/offline device records

docs/API_MESSAGING_IN_APP.md

@@ -0,0 +1,173 @@
+# In-app Notifications API
+
+Manage in-app notifications for users. Notifications can be written, retrieved, marked as read, or deleted.
+
+---
+
+### Write Notification
+
+* **POST** `/messaging/in-app/write` → Create a new in-app notification.
+
+  **Request Body:**
+
+  ```json
+  {
+    "content": "This is a test notification",
+    "level": "alert"   // optional, ["interrupt","info","alert"]  default: "alert"
+  }
+  ```
+
+  **Response:**
+
+  ```json
+  {
+    "success": true
+  }
+  ```
+
+#### `curl` Example
+
+```bash
+curl -X POST "http://<server_ip>:<GRAPHQL_PORT>/messaging/in-app/write" \
+  -H "Authorization: Bearer <API_TOKEN>" \
+  -H "Accept: application/json" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "content": "This is a test notification",
+    "level": "alert"
+  }'
+```
+
+---
+
+### Get Unread Notifications
+
+* **GET** `/messaging/in-app/unread` → Retrieve all unread notifications.
+
+  **Response:**
+
+  ```json
+  [
+    {
+      "timestamp": "2025-10-10T12:34:56",
+      "guid": "f47ac10b-58cc-4372-a567-0e02b2c3d479",
+      "read": 0,
+      "level": "alert",
+      "content": "This is a test notification"
+    }
+  ]
+  ```
+
+#### `curl` Example
+
+```bash
+curl -X GET "http://<server_ip>:<GRAPHQL_PORT>/messaging/in-app/unread" \
+  -H "Authorization: Bearer <API_TOKEN>" \
+  -H "Accept: application/json"
+```
+
+---
+
+### Mark All Notifications as Read
+
+* **POST** `/messaging/in-app/read/all` → Mark all notifications as read.
+
+  **Response:**
+
+  ```json
+  {
+    "success": true
+  }
+  ```
+
+#### `curl` Example
+
+```bash
+curl -X POST "http://<server_ip>:<GRAPHQL_PORT>/messaging/in-app/read/all" \
+  -H "Authorization: Bearer <API_TOKEN>" \
+  -H "Accept: application/json"
+```
+
+---
+
+### Mark Single Notification as Read
+
+* **POST** `/messaging/in-app/read/<guid>` → Mark a single notification as read using its GUID.
+
+  **Response (success):**
+
+  ```json
+  {
+    "success": true
+  }
+  ```
+
+  **Response (failure):**
+
+  ```json
+  {
+    "success": false,
+    "error": "Notification not found"
+  }
+  ```
+
+#### `curl` Example
+
+```bash
+curl -X POST "http://<server_ip>:<GRAPHQL_PORT>/messaging/in-app/read/f47ac10b-58cc-4372-a567-0e02b2c3d479" \
+  -H "Authorization: Bearer <API_TOKEN>" \
+  -H "Accept: application/json"
+```
+
+---
+
+### Delete All Notifications
+
+* **DELETE** `/messaging/in-app/delete` → Remove all notifications from the system.
+
+  **Response:**
+
+  ```json
+  {
+    "success": true
+  }
+  ```
+
+#### `curl` Example
+
+```bash
+curl -X DELETE "http://<server_ip>:<GRAPHQL_PORT>/messaging/in-app/delete" \
+  -H "Authorization: Bearer <API_TOKEN>" \
+  -H "Accept: application/json"
+```
+
+---
+
+### Delete Single Notification
+
+* **DELETE** `/messaging/in-app/delete/<guid>` → Remove a single notification by its GUID.
+
+  **Response (success):**
+
+  ```json
+  {
+    "success": true
+  }
+  ```
+
+  **Response (failure):**
+
+  ```json
+  {
+    "success": false,
+    "error": "Notification not found"
+  }
+  ```
+
+#### `curl` Example
+
+```bash
+curl -X DELETE "http://<server_ip>:<GRAPHQL_PORT>/messaging/in-app/delete/f47ac10b-58cc-4372-a567-0e02b2c3d479" \
+  -H "Authorization: Bearer <API_TOKEN>" \
+  -H "Accept: application/json"
+```