chore: drop dead code, export routeTree

Removes the orphaned generated OpenAPI client (superseded by the
hand-written client.ts), the unrouted AudioTab, and app/'s unused
standalone entry (main.tsx, index.html, vite.config) — app/ is a
shared library consumed by web/ and tauri/. routeTree is exported so
tests can build routers over memory history.

app/package.json

@@ -4,10 +4,7 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "dev": "vite",
-    "build": "vite build",
     "typecheck": "tsc -p tsconfig.json --noEmit",
-    "preview": "vite preview",
     "lint": "biome lint src",
     "lint:fix": "biome lint --write src",
     "format": "biome format --write src",