build(docker): bump node from 25-alpine to 26-alpine

Apply Dependabot PR #149 to keep the test container image on a supported Node.js release.

Author: sergak01

Dockerfile

@@ -1,5 +1,5 @@
 # Use official Node.js image
-FROM node:25-alpine
+FROM node:26-alpine
 
 # Set working directory
 WORKDIR /app