Fix Resend API key error during build

- Move Resend client instantiation from module level to function
- Add validation to skip placeholder API keys
- Set empty RESEND_API_KEY and GOOGLE_SERVICE_ACCOUNT_JSON during build

Dockerfile.coolify

@@ -0,0 +1,36 @@
+# Dockerfile simplificado para Coolify
+FROM node:20-alpine
+
+WORKDIR /app
+
+# Instalar dependencias
+COPY package.json package-lock.json ./
+RUN npm ci --ignore-scripts
+
+# Copiar código fuente
+COPY . .
+
+# Variables de entorno
+ENV NEXT_TELEMETRY_DISABLED=1
+ENV NODE_ENV=production
+ENV NEXT_PUBLIC_SUPABASE_URL=https://placeholder.supabase.co
+ENV NEXT_PUBLIC_SUPABASE_ANON_KEY=placeholder-anon-key
+
+# Aumentar memoria para build
+ENV NODE_OPTIONS="--max-old-space-size=4096"
+
+# Build
+RUN npm run build
+
+# Configurar usuario
+RUN addgroup --system --gid 1001 nodejs
+RUN adduser --system --uid 1001 nextjs
+
+USER nextjs
+
+EXPOSE 3000
+
+ENV PORT=3000
+ENV HOSTNAME="0.0.0.0"
+
+CMD ["npm", "start"]