fix: resolve all Docker build errors

- pnpm: remove separate deps stage (cross-stage copy breaks virtual store links)
- Add .dockerignore (node_modules, .next, secrets)
- map-client.tsx: escape apostrophe, use Link instead of <a>
- cron/review-digest/route.ts: unexport signUserId (invalid Next.js route export)
- auth.ts: guard user.id undefined before eq() call
- queries.ts: fix swapped lte(Date, column) → gte(column, Date) (×2)
- Dockerfile: drop COPY public/ (directory doesn't exist)

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

.dockerignore

@@ -0,0 +1,5 @@
+.next
+node_modules
+.env.local
+.env.prod
+.git