fix: add lightweight migrate Dockerfile target to avoid tsup build failure in CI

The migrate service only needs Prisma CLI to run 'prisma db push'. Previously
it used the 'builder' target which runs 'npx turbo build' (including sdk-ts
needing tsup), causing failures in fresh CI builds over TCP where Docker cache
is unavailable. New 'migrate' target copies only node_modules and prisma schema.

Dockerfile

@@ -16,6 +16,10 @@ COPY . .
 RUN npx prisma generate --schema=packages/database/prisma/schema.prisma
 RUN npx turbo build
 
+FROM base AS migrate
+COPY --from=deps /app/node_modules ./node_modules
+COPY packages/database/prisma ./packages/database/prisma
+
 FROM base AS web
 RUN addgroup --system --gid 1001 nodejs && \
     adduser --system --uid 1001 nextjs