docs(api): align auth/devices/libraries/media-items docs with handlers

Verified against the Echo routes and handler structs, fixing drift that
would break API clients:

- login: response field is access_token, not token (AuthResponse struct)
- register status: status is only pending|approved; expiry is HTTP 410
  (not a status value), approved responses are single-use, and pending
  registrations do not survive server restarts
- visible libraries: endpoint is GET /api/libraries/visibility and
  returns a top-level array of full library rows, not a wrapped object
- media items list: response is {"data": [...]}, library_id is optional,
  limit defaults to 50 (max 1000), no total field; document the sort
  parameter, the two response shapes, and raw-vs-resolved file paths

refresh and device-registration docs verified accurate; no changes.

docs/developer/api/libraries/get_visible_libraries.md

@@ -2,7 +2,7 @@
 
 Retrieve all libraries visible to the current user.
 
-**Endpoint**: `GET /api/libraries/visible`
+**Endpoint**: `GET /api/libraries/visibility`
 **Auth**: Required
 
 ## Request Headers
@@ -14,26 +14,33 @@ Retrieve all libraries visible to the current user.
 ### Example Request
 
 ```http
-GET /api/libraries/visible
+GET /api/libraries/visibility
 Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
 ```
 
 ## Response (200 OK)
 
+A top-level JSON **array** of library rows:
+
 ```json
-{
-  "libraries": [
-    {
-      "id": "uuid",
-      "name": "My Ebooks",
-      "description": "Ebook collection",
-      "type_name": "ebooks",
-      "is_visible": true
-    }
-  ]
-}
+[
+  {
+    "id": "uuid",
+    "name": "My Ebooks",
+    "description": "Ebook collection",
+    "library_type_id": "uuid",
+    "created_by_admin_id": "uuid",
+    "created_at": "2026-01-31T10:00:00Z",
+    "updated_at": "2026-01-31T10:00:00Z",
+    "type_name": "ebooks",
+    "type_description": "Ebook libraries",
+    "is_visible": true
+  }
+]
 ```
 
+Nullable columns (`description`, `type_description`) serialize as `null` when unset. Timestamps are RFC 3339.
+
 ## Error Responses
 
 | Code | Description              |