feat: improve Docker deployment and Dify API configuration

- Use environment variables for Dify API key/URL
- Add host.docker.internal support in docker-compose
- Add DATABASE_URL env and prisma db push to Dockerfile
- Clean up test/requirement files and add deployment docs

app/api/chat/route.ts

@@ -1,8 +1,8 @@
 import { NextResponse } from "next/server"
 import { prisma } from "@/app/lib/prisma"
 
-const FALLBACK_API_KEY = 'app-lbe2lglt7taGtZk0dG7pAhbx'
-const FALLBACK_API_URL = 'http://df.clkeji.com/v1/chat-messages'
+const FALLBACK_API_KEY = process.env.DIFY_API_KEY || 'app-lbe2lglt7taGtZk0dG7pAhbx'
+const FALLBACK_API_URL = process.env.DIFY_API_URL || 'http://host.docker.internal/v1/chat-messages'
 
 export async function POST(request: Request) {
   try {