feat(auth): add Discord OAuth sign-in and user timezones

Add persistent user and session storage, protected profile requests, and React sign-in controls. Capture and preserve each user's timezone, and load development and production configuration before migrations and server startup.

src/App.tsx

@@ -1,4 +1,5 @@
 import { Route, Routes, useLocation, useNavigate } from "react-router";
+import { AuthControls } from "./components/AuthControls";
 import { Home } from "./pages/Home";
 import { About } from "./pages/About";
 import { Settings } from "./pages/Settings";
@@ -14,6 +15,7 @@ export function App() {
         <button type="button" disabled={pathname === "/about"} onClick={() => navigate("/about")}>About</button>{" "}
         <button type="button" disabled={pathname === "/settings"} onClick={() => navigate("/settings")}>Settings</button>
       </nav>
+      <AuthControls />
       <main>
         <Routes>
           <Route path="/" element={<Home />} />