feat: add admin user initialization endpoint with request handling

apps/api/swagger.json

@@ -9,6 +9,40 @@
     "version": "0.1.0"
   },
   "paths": {
+    "/api/auth/init_admin": {
+      "post": {
+        "tags": [
+          "Authentication"
+        ],
+        "summary": "Initializes the admin user",
+        "description": "Initializes the admin user if no admin user exists and the correct setup secret is provided.",
+        "operationId": "init_admin",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/AdminInitRequest"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "200": {
+            "description": "Admin user initialized successfully"
+          },
+          "400": {
+            "description": "Invalid request payload"
+          },
+          "401": {
+            "description": "Unauthorized: Admin user already exists or invalid setup secret"
+          },
+          "500": {
+            "description": "Internal server error"
+          }
+        }
+      }
+    },
     "/api/auth/login": {
       "post": {
         "tags": [
@@ -75,6 +109,26 @@
   },
   "components": {
     "schemas": {
+      "AdminInitRequest": {
+        "type": "object",
+        "description": "Login request payload",
+        "required": [
+          "username",
+          "password",
+          "setup_secret"
+        ],
+        "properties": {
+          "password": {
+            "type": "string"
+          },
+          "setup_secret": {
+            "type": "string"
+          },
+          "username": {
+            "type": "string"
+          }
+        }
+      },
       "HealthInfo": {
         "type": "object",
         "description": "System health information",