Fix Live Activity lock screen rendering and polish multi-account auth.

Flatten widget layouts and use system colors so banner and expanded regions render on vibrant lock screens; migrate auth sessions per account to prevent double sign-in; scope app lock PIN to accounts; default clock description to "Clock In"; add architecture docs and deferred form validation on auth screens.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/_layout.tsx

@@ -12,7 +12,7 @@ import {
 import { useFonts } from "expo-font";
 import * as SplashScreen from "expo-splash-screen";
 import { useEffect, type ReactNode } from "react";
-import { Platform, View } from "react-native";
+import { View } from "react-native";
 import { StatusBar } from "expo-status-bar";
 import "react-native-reanimated";
 import { SafeAreaProvider } from "react-native-safe-area-context";
@@ -23,8 +23,6 @@ import { AccountsProvider, useAccounts } from "@/contexts/AccountsContext";
 import { AuthProvider, useSession } from "@/contexts/AuthContext";
 import { ThemeProvider, useAppTheme } from "@/contexts/ThemeContext";
 import { TRPCProvider } from "@/lib/trpc";
-import { ensureWidgetBrandAssets } from "@/lib/widget-brand-assets";
-
 export { ErrorBoundary } from "expo-router";
 
 SplashScreen.preventAutoHideAsync();
@@ -77,12 +75,6 @@ export default function RootLayout() {
     }
   }, [loaded]);
 
-  useEffect(() => {
-    if (Platform.OS === "ios") {
-      void ensureWidgetBrandAssets();
-    }
-  }, []);
-
   if (!loaded) {
     return null;
   }