fix: add .dockerignore — exclude 7GB+ from demo build context

.dockerignore

@@ -0,0 +1,12 @@
+# Ignore everything except what the demo Dockerfiles need
+*
+
+# Allow neode-ui (frontend + mock backend + docker configs)
+!neode-ui/
+
+# Allow demo assets (AIUI pre-built dist)
+!demo/
+
+# Exclude nested node_modules (will npm install in container)
+neode-ui/node_modules
+neode-ui/dist