Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/vite.config.ts

@@ -0,0 +1,23 @@
+/// <reference types="vitest" />
+import react from "@vitejs/plugin-react";
+import { defineConfig } from "vite";
+
+// SPEC dev-environment §5: Vite dev proxy /api -> :8000 with ws:true for /api/ws.
+export default defineConfig({
+  plugins: [react()],
+  server: {
+    port: 5173,
+    proxy: {
+      "/api": {
+        target: "http://127.0.0.1:8000",
+        changeOrigin: true,
+        ws: true,
+      },
+    },
+  },
+  test: {
+    environment: "jsdom",
+    globals: true,
+    setupFiles: ["./src/test/setup.ts"],
+  },
+});