Update the application to use port 3000 across all services

Adjusts port configurations from 5000 to 3000 in .replit, Dockerfile, docker-compose.yml, replit.md and server/index.ts for consistent service deployment.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: dec54137-d5a2-4406-8ad4-5f2f9fb110bf
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/0715008c-7244-40f4-befc-26c014852236/5d315300-98fa-429a-abb0-4fdce6a2e3c9.jpg

server/index.ts

@@ -58,10 +58,9 @@ app.use((req, res, next) => {
     serveStatic(app);
   }
 
-  // ALWAYS serve the app on port 5000
+  // ALWAYS serve the app on port 3000
   // this serves both the API and the client.
-  // It is the only port that is not firewalled.
-  const port = 5000;
+  const port = process.env.PORT ? parseInt(process.env.PORT) : 3000;
   server.listen({
     port,
     host: "0.0.0.0",