fix(docker): provide build-time auth/db env to next build

next build collects page data for /api/auth/[...nextauth] and aborts
when NEXTAUTH_URL/SECRET/DATABASE_URL are unset. The CI Build job
sets these as env vars; Dockerfile.prod did not, so the prod image
build failed during Release Images even though plain build worked.

Add ARG defaults that mirror the CI placeholders. Real values are
injected at container start, so build-time placeholders are inert.

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

Dockerfile.prod

@@ -44,6 +44,21 @@ RUN pnpm --filter @capakraken/db db:generate
 # Build the Next.js application
 ENV NEXT_TELEMETRY_DISABLED=1
 ENV NODE_ENV=production
+# next build collects page data for /api/auth/[...nextauth] which crashes
+# without these envs even though they are placeholders at image-build time
+# (real values are injected at container start). Mirrors the CI build job.
+ARG NEXTAUTH_URL=http://localhost:3100
+ARG AUTH_URL=http://localhost:3100
+ARG NEXTAUTH_SECRET=ci-build-placeholder-secret-minimum-32-chars
+ARG AUTH_SECRET=ci-build-placeholder-secret-minimum-32-chars
+ARG DATABASE_URL=postgresql://placeholder:placeholder@localhost:5432/placeholder
+ARG REDIS_URL=redis://placeholder:6379
+ENV NEXTAUTH_URL=$NEXTAUTH_URL
+ENV AUTH_URL=$AUTH_URL
+ENV NEXTAUTH_SECRET=$NEXTAUTH_SECRET
+ENV AUTH_SECRET=$AUTH_SECRET
+ENV DATABASE_URL=$DATABASE_URL
+ENV REDIS_URL=$REDIS_URL
 RUN pnpm --filter @capakraken/web build
 
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