init: FileDrop phase1 architecture and scaffold

- Rust axum signaling server with WebSocket support
- Lit + TypeScript frontend with Vite
- Redis session storage with TTL
- WebRTC transport and crypto client stubs
- Phase1 architecture plan in plans/
- Deploy directory structure prepared

web/vite.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+  build: {
+    outDir: '../server/static',
+    emptyOutDir: true,
+  },
+  server: {
+    proxy: {
+      '/api': 'http://localhost:3000',
+      '/ws': {
+        target: 'ws://localhost:3000',
+        ws: true,
+      },
+    },
+  },
+});