feat: initial project setup

- FastAPI backend (Python 3.12, uv)
- React 19 + TypeScript + Vite frontend
- Devcontainer with Node 22, Python 3.12, uv, opencode
- Basic app structure and project docs

frontend/vite.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from "vite";
+import react from "@vitejs/plugin-react";
+
+export default defineConfig({
+  plugins: [react()],
+  server: {
+    port: 3000,
+    proxy: {
+      "/api": {
+        target: "http://localhost:8000",
+        changeOrigin: true,
+      },
+    },
+  },
+});