Initial scaffold: Flask/SQLite backend, React/Vite PWA frontend

Backend: receipt upload -> LLM vision extraction (OpenAI-compatible,
provider-agnostic), item review/edit, per-group splitting against
Cospend projects/members, highlight+upload via WebDAV, public share
link, bill creation via Cospend's OCS API (verified against real
source, not just doc summaries).

Frontend: capture -> review -> group -> summary flow as an installable
PWA.

install.sh / run.sh (venv + npm, tmux session) instead of Docker, per
the ~/Projects/gain pattern.

frontend/vite.config.ts

@@ -0,0 +1,30 @@
+import react from '@vitejs/plugin-react'
+import { defineConfig } from 'vite'
+import { VitePWA } from 'vite-plugin-pwa'
+
+// https://vite.dev/config/
+export default defineConfig({
+  plugins: [
+    react(),
+    VitePWA({
+      registerType: 'autoUpdate',
+      manifest: {
+        name: 'wgBill',
+        short_name: 'wgBill',
+        description: 'Photograph a receipt, split it, bill it via Cospend',
+        theme_color: '#1a1a1a',
+        background_color: '#1a1a1a',
+        display: 'standalone',
+        icons: [
+          { src: 'pwa-192x192.png', sizes: '192x192', type: 'image/png' },
+          { src: 'pwa-512x512.png', sizes: '512x512', type: 'image/png' },
+        ],
+      },
+    }),
+  ],
+  server: {
+    proxy: {
+      '/api': 'http://localhost:5000',
+    },
+  },
+})