feat: add theme system with light/dark mode support

- Add ThemeStore (Zustand) for reactive theme switching
- Add Themes.tsx with THEMES object (defaultLight, defaultDark)
- Add Settings screen with theme switcher and logout button
- Add BaseButton component for reusable themed buttons
- Migrate all components from static currentTheme to useThemeStore()
- Add shadowColor to theme (iOS only, Android uses elevation)
- All text elements now use theme colors (textPrimary, textSecondary, etc.)
- Update tab navigation to include Settings tab
- Move logout from Header to Settings screen

apps/client/src/app/note/[id].tsx

@@ -1,9 +1,11 @@
 import { View, Text, TextInput, Pressable } from "react-native";
 import { useLocalSearchParams } from "expo-router";
 import BaseBackground from "../../components/BaseBackground";
+import { useThemeStore } from "../../stores/ThemeStore";
 
 const NoteScreen = () => {
   const { id } = useLocalSearchParams<{ id: string }>();
+  const { theme } = useThemeStore();
 
   // TODO: Fetch event by id using EventService.getById()
   // TODO: Display and edit the event's note field
@@ -15,16 +17,18 @@ const NoteScreen = () => {
   return (
     <BaseBackground>
       <View className="flex-1 p-4">
-        <Text className="text-2xl mb-4">Note</Text>
-        <Text className="text-gray-500 mb-4">Event ID: {id}</Text>
+        <Text className="text-2xl mb-4" style={{ color: theme.textPrimary }}>Note</Text>
+        <Text className="mb-4" style={{ color: theme.textSecondary }}>Event ID: {id}</Text>
         <TextInput
           placeholder="Write your note here..."
+          placeholderTextColor={theme.textMuted}
           multiline
           className="w-full border rounded p-2 flex-1 mb-4"
           textAlignVertical="top"
+          style={{ color: theme.textPrimary, borderColor: theme.borderPrimary, backgroundColor: theme.secondaryBg }}
         />
-        <Pressable className="bg-blue-500 p-3 rounded">
-          <Text className="text-white text-center">Save Note</Text>
+        <Pressable className="p-3 rounded" style={{ backgroundColor: theme.confirmButton }}>
+          <Text className="text-center" style={{ color: theme.buttonText }}>Save Note</Text>
         </Pressable>
       </View>
     </BaseBackground>