Exclude nested node_modules from the Docker build context

.dockerignore only matched the root node_modules, so a locally
installed frontend-modern/node_modules entered the build context and
collided with the npm ci layer during COPY frontend-modern/, failing
local image builds. CI checkouts never hit this because they build
from a clean tree.

.dockerignore

@@ -29,6 +29,7 @@ scripts/macos/dist/
 
 # Dependencies
 node_modules/
+**/node_modules/
 vendor/
 
 # Logs