Add host configuration for backend server and update documentation

- Introduced a new `host` option in `flake.nix` to specify the server's bind address, defaulting to `0.0.0.0`.
- Updated `run.sh` to use the `HOST` environment variable for server binding.
- Modified `config.py` to read the `HOST` from environment variables, defaulting to `0.0.0.0`.
- Enhanced `README.md` with instructions for setting up the `HOST` variable and clarified access details for development and production modes.
- Adjusted `vite.config.ts` to allow frontend access from other computers by default.

frontend/vite.config.ts

@@ -1,19 +1,26 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 
+// Get backend URL from environment variables (for dev server proxy)
+const backendHost = process.env.VITE_BACKEND_HOST || '127.0.0.1'
+const backendPort = process.env.VITE_BACKEND_PORT || '8080'
+const backendUrl = `http://${backendHost}:${backendPort}`
+
 export default defineConfig({
   plugins: [react()],
   build: {
     outDir: 'dist',
   },
   server: {
+    host: '0.0.0.0', // Allow access from other computers
+    port: parseInt(process.env.VITE_PORT || '5173'),
     proxy: {
       '/api': {
-        target: 'http://127.0.0.1:8080',
+        target: backendUrl,
         changeOrigin: true,
       },
       '/admin': {
-        target: 'http://127.0.0.1:8080',
+        target: backendUrl,
         changeOrigin: true,
       },
     },