feat: production-ready UI with onboarding wizard and dashboard

- Onboarding flow (welcome -> Codex setup -> Claude setup -> done) with
  dark-themed screens and step indicators; completion stored in SecureStore
- Smart root redirect checks onboarding state on launch
- Dashboard tab shows both services at a glance via ServiceStatusCard;
  useFocusEffect + reload() keeps it fresh when credentials change in tabs
- Settings tab manages credentials and exposes re-run setup wizard
- Polished Codex and Claude detail screens with service headers and empty states
- 4-tab layout (Home, Codex, Claude, Settings) with dark-mode tab bar
- Both hooks gain reload() for cross-tab credential refresh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/(tabs)/_layout.tsx

@@ -1,16 +1,39 @@
 import { Tabs } from "expo-router";
+import { useColorScheme } from "react-native";
 import { MaterialIcons } from "@expo/vector-icons";
 
 export default function TabLayout() {
+  const colorScheme = useColorScheme();
+  const isDark = colorScheme === "dark";
+
   return (
     <Tabs
       screenOptions={{
+        headerShown: false,
         tabBarActiveTintColor: "#10a37f",
-        tabBarStyle: { backgroundColor: "#ffffff" },
-        headerStyle: { backgroundColor: "#ffffff" },
-        headerTitleStyle: { fontWeight: "600" },
+        tabBarInactiveTintColor: isDark ? "#52525b" : "#a1a1aa",
+        tabBarStyle: {
+          backgroundColor: isDark ? "#09090b" : "#ffffff",
+          borderTopColor: isDark ? "#27272a" : "#f4f4f5",
+          height: 56,
+          paddingBottom: 8,
+          paddingTop: 6,
+        },
+        tabBarLabelStyle: {
+          fontSize: 10,
+          fontWeight: "600",
+        },
       }}
     >
+      <Tabs.Screen
+        name="index"
+        options={{
+          title: "Home",
+          tabBarIcon: ({ color, size }) => (
+            <MaterialIcons name="home" size={size} color={color} />
+          ),
+        }}
+      />
       <Tabs.Screen
         name="codex"
         options={{
@@ -29,6 +52,15 @@ export default function TabLayout() {
           ),
         }}
       />
+      <Tabs.Screen
+        name="settings"
+        options={{
+          title: "Settings",
+          tabBarIcon: ({ color, size }) => (
+            <MaterialIcons name="settings" size={size} color={color} />
+          ),
+        }}
+      />
     </Tabs>
   );
 }