feat: optimize Docker startup with Next.js standalone output and proper migrations

- Add `output: standalone` to next.config.js for faster cold start
- Rebuild runner stage around standalone bundle (node server.js instead of pnpm start)
- Replace prisma db push with prisma migrate deploy (proper migration workflow)
- Remove npx/pnpm at runtime, use direct binary paths
- Add HOSTNAME=0.0.0.0 for standalone server to listen on all interfaces
- Fix next.config.js not copied in builder stage
- Update README: pnpm instead of yarn, correct ports, full env vars documentation

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

docker-entrypoint.sh

@@ -1,15 +1,11 @@
 #!/bin/sh
 set -e
 
-echo "📁 Ensuring data directory exists..."
-mkdir -p /app/data
-
-echo "🔄 Pushing Prisma schema to database..."
-npx prisma db push --skip-generate --accept-data-loss
+echo "🔄 Applying database migrations..."
+./node_modules/.bin/prisma migrate deploy
 
 echo "🔧 Initializing database..."
 node scripts/init-db.mjs
 
 echo "🚀 Starting application..."
-exec pnpm start
-
+exec node server.js