build(docs): pin docs builder image to node 25.1 (#714)

## 📝 Description

Pinned the docs build stage to node:25.1 so Docker no longer pulls
latest. This avoids the breaking change introduced in Node 25.2. Adds
also the missing reference
`reference/os-ubuntu-images/ubuntu-2404-arm-image`.

Check [the issue](renderedtext/tasks#8917).

## ✅ Checklist
- [x] I have tested this change
- [x] ~This change requires documentation update~ N/A

Author: dexyk

docs/Dockerfile

@@ -1,7 +1,7 @@
 ARG RUNNER_IMAGE=nginx
 
 # Build stage
-FROM node AS builder
+FROM node:25.1 AS builder
 WORKDIR /app
 
 COPY package.json package.json
@@ -44,5 +44,3 @@ WORKDIR /app
 
 ADD default.conf /etc/nginx/conf.d/default.conf
 COPY --from=builder /app/build/ /usr/share/nginx/html/
-
-

docs/sidebars.js

@@ -82,7 +82,7 @@ const sidebars = {
           'using-semaphore/tasks',
         ]
       },
-      
+
 
       {
         type: 'category',
@@ -95,7 +95,7 @@ const sidebars = {
           }
         ]
       },
-      
+
 
       {
         type: 'category',
@@ -197,7 +197,8 @@ const sidebars = {
               'reference/os-ubuntu-images/ubuntu-2004-image',
               'reference/os-ubuntu-images/ubuntu-2204-image',
               'reference/os-ubuntu-images/ubuntu-2204-arm-image',
-              'reference/os-ubuntu-images/ubuntu-2404-image'
+              'reference/os-ubuntu-images/ubuntu-2404-image',
+              'reference/os-ubuntu-images/ubuntu-2404-arm-image'
             ]
           },
         ]