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/components/EventConfirmDialog.tsx

@@ -1,5 +1,6 @@
 import { View, Text, Modal, Pressable } from "react-native";
 import { CreateEventDTO } from "@calchat/shared";
+import { useThemeStore } from "../stores/ThemeStore";
 
 type EventConfirmDialogProps = {
   visible: boolean;
@@ -16,6 +17,8 @@ const EventConfirmDialog = ({
   onReject: _onReject,
   onClose: _onClose,
 }: EventConfirmDialogProps) => {
+  const { theme } = useThemeStore();
+
   // TODO: Display proposed event details (title, time, description)
   // TODO: Confirm button calls onConfirm and closes dialog
   // TODO: Reject button calls onReject and closes dialog
@@ -26,7 +29,7 @@ const EventConfirmDialog = ({
     <Modal visible={false} transparent animationType="fade">
       <View>
         <Pressable>
-          <Text>EventConfirmDialog - Not Implemented</Text>
+          <Text style={{ color: theme.textPrimary }}>EventConfirmDialog - Not Implemented</Text>
         </Pressable>
       </View>
     </Modal>