Fix mobile white screen: stop Outlet Date.now() remount loop (#54) (#56)

## Summary

- Follow-up for #54 (localStorage guard in #55 did not fix mobile white screen)
- Confirmed in production bundle: `ProtectedRoutes` rendered `<Outlet key={Date.now()} />`
- That remounts the entire authenticated tree on **every** parent re-render (account fetch, WebSocket connect/status, conversations, messages)
- On mobile this shows as: brief UI flash → solid white page (matches screen recording)
- Also memoize styled-components theme in `GlobalThemeWrapper` so `ParticleBackground` does not tear down/restart its canvas on unrelated re-renders

## Evidence

Production JS currently contains:
```js
e?(0,ma.jsx)(a.sv,{},Date.now()):(0,ma.jsx)(a.C5,{to:"/signin/",replace:!0})
```
i.e. authenticated → `<Outlet key={Date.now()} />`

## Test plan

- [ ] Mobile Vivaldi/Chrome: sign in on hesychia.ai → dashboard stays visible (header, conversations toggle, input)
- [ ] Pull-to-refresh while logged in → UI returns and stays
- [ ] Desktop login still works; switching conversations / WS reconnect does not blank the page
- [ ] Open mobile menu / Conversations sidebar still worksReviewed-on: #56

llm-fe/src/App.tsx

@@ -34,7 +34,7 @@ const ProtectedRoutes = () => {
   if (!authenticated) return <Navigate to='/signin/' replace />
   //if(!needsNewPassword) return <Navigate to='/password_reset/' replace/>
 
-  return <Outlet key={Date.now()} />
+  return <Outlet />
 }