Fix: pass NEXT_PUBLIC_BASE_PATH build arg through Dockerfile

Declares ARG NEXT_PUBLIC_BASE_PATH in builder stage and passes it
inline to pnpm build so Next.js basePath is applied at compile time.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -12,6 +12,7 @@ ARG CI
 ARG BUILDTIME
 ARG VERSION
 ARG REVISION
+ARG NEXT_PUBLIC_BASE_PATH
 ENV CI=$CI
 
 # Install and build only outside CI
@@ -22,6 +23,7 @@ RUN if [ "$CI" != "true" ]; then \
       NEXT_PUBLIC_BUILDTIME=$BUILDTIME \
       NEXT_PUBLIC_VERSION=$VERSION \
       NEXT_PUBLIC_REVISION=$REVISION \
+      NEXT_PUBLIC_BASE_PATH=$NEXT_PUBLIC_BASE_PATH \
       pnpm run build; \
     else \
       echo "✅ Using prebuilt app from CI context"; \