fix: configure nginx proxy for API calls to fix cross-origin issues

Problem:
Frontend was calling localhost:8000 for API, but when accessing
from Windows (192.168.254.79:8888), the browser tried to connect
to localhost on the Windows machine instead of the server.

Solution:
1. Added nginx.conf with proxy configuration for /api/ routes
2. Updated Dockerfile to copy nginx.conf to container
3. Changed api.ts baseURL from 'http://localhost:8000/api/v1' to '/api/v1'
4. Nginx now proxies all /api/ requests to backend:8000

This allows the frontend to work correctly from any client
by using relative paths that nginx proxies to the backend.

frontend/src/lib/api.ts

@@ -1,7 +1,7 @@
 import axios from 'axios';
 
 const api = axios.create({
-  baseURL: import.meta.env.VITE_API_URL || 'http://localhost:8000/api/v1',
+  baseURL: '/api/v1',
   headers: {
     'Content-Type': 'application/json',
   },