proxy: add unload of single model (#318)

This adds a new API endpoint, /api/models/unload/*model, that unloads a single model. In the UI when a model is in a ReadyState it will have a new button to unload it. 

Fixes #312

ui/vite.config.ts

@@ -15,6 +15,7 @@ export default defineConfig({
       "/api": "http://localhost:8080", // Proxy API calls to Go backend during development
       "/logs": "http://localhost:8080",
       "/upstream": "http://localhost:8080",
+      "/unload": "http://localhost:8080",
     },
   },
 });