Fix: Use ARG for NEXT_PUBLIC variables to ensure correct API URL during build

Problem: Frontend was trying to contact http://localhost:8080 instead of
https://api.lions.dev/btpxpress because NEXT_PUBLIC_API_URL wasn't correctly
baked into the Next.js bundle during build.

Solution:
- Added ARG declarations with correct default values for all NEXT_PUBLIC_* variables
- Convert ARG to ENV before running npm run build
- This ensures Next.js bakes the correct values into the bundle
- ARG allows override at docker build time if needed
- Fixed ENV format to use = instead of space (removes Docker warnings)

Variables defined:
- NEXT_PUBLIC_API_URL=https://api.lions.dev/btpxpress
- NEXT_PUBLIC_KEYCLOAK_URL=https://security.lions.dev
- NEXT_PUBLIC_KEYCLOAK_REALM=btpxpress
- NEXT_PUBLIC_KEYCLOAK_CLIENT_ID=btpxpress-frontend
- NEXT_PUBLIC_APP_ENV=production

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Dockerfile

@@ -19,17 +19,31 @@ RUN npm ci
 
 COPY . .
 
+# Build arguments for NEXT_PUBLIC variables (can be overridden at build time)
+ARG NEXT_PUBLIC_API_URL=https://api.lions.dev/btpxpress
+ARG NEXT_PUBLIC_KEYCLOAK_URL=https://security.lions.dev
+ARG NEXT_PUBLIC_KEYCLOAK_REALM=btpxpress
+ARG NEXT_PUBLIC_KEYCLOAK_CLIENT_ID=btpxpress-frontend
+ARG NEXT_PUBLIC_APP_ENV=production
+
+# Convert ARG to ENV for Next.js build process
+ENV NEXT_PUBLIC_API_URL=${NEXT_PUBLIC_API_URL}
+ENV NEXT_PUBLIC_KEYCLOAK_URL=${NEXT_PUBLIC_KEYCLOAK_URL}
+ENV NEXT_PUBLIC_KEYCLOAK_REALM=${NEXT_PUBLIC_KEYCLOAK_REALM}
+ENV NEXT_PUBLIC_KEYCLOAK_CLIENT_ID=${NEXT_PUBLIC_KEYCLOAK_CLIENT_ID}
+ENV NEXT_PUBLIC_APP_ENV=${NEXT_PUBLIC_APP_ENV}
+
 # Build Next.js application
-ENV NODE_ENV production
-ENV NEXT_TELEMETRY_DISABLED 1
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
 RUN npm run build
 
 ## Stage 3: Production image
 FROM node:20-alpine AS runner
 WORKDIR /app
 
-ENV NODE_ENV production
-ENV NEXT_TELEMETRY_DISABLED 1
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
 
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs
@@ -43,8 +57,8 @@ USER nextjs
 
 EXPOSE 3000
 
-ENV PORT 3000
-ENV HOSTNAME "0.0.0.0"
+ENV PORT=3000
+ENV HOSTNAME="0.0.0.0"
 
 # Health check
 HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \