refactor: add CardBase and ModalBase components

- Add CardBase: reusable card with header, content, footer
  - Configurable via props: padding, border, text size, background
- Add ModalBase: modal wrapper using CardBase internally
  - Provides backdrop, click-outside-to-close, Android back button
- Refactor EventCardBase to use CardBase
- Refactor DeleteEventModal to use ModalBase
- Refactor EventOverlay (calendar.tsx) to use ModalBase
- Update CLAUDE.md with component documentation

apps/client/src/components/ModalBase.tsx

@@ -0,0 +1,74 @@
+import { Modal, Pressable } from "react-native";
+import { ReactNode } from "react";
+import { useThemeStore } from "../stores/ThemeStore";
+import { CardBase } from "./CardBase";
+
+type ModalBaseProps = {
+  visible: boolean;
+  onClose: () => void;
+  title: string;
+  subtitle?: string;
+  children: ReactNode;
+  footer?: {
+    label: string;
+    onPress: () => void;
+  };
+  scrollable?: boolean;
+  maxContentHeight?: number;
+};
+
+export const ModalBase = ({
+  visible,
+  onClose,
+  title,
+  subtitle,
+  children,
+  footer,
+  scrollable,
+  maxContentHeight,
+}: ModalBaseProps) => {
+  const { theme } = useThemeStore();
+
+  return (
+    <Modal
+      visible={visible}
+      transparent={true}
+      animationType="fade"
+      onRequestClose={onClose}
+    >
+      <Pressable
+        className="flex-1 justify-center items-center"
+        style={{ backgroundColor: "rgba(0,0,0,0.5)" }}
+        onPress={onClose}
+      >
+        <Pressable
+          className="w-11/12 rounded-2xl overflow-hidden"
+          style={{
+            backgroundColor: theme.primeBg,
+            borderWidth: 4,
+            borderColor: theme.borderPrimary,
+          }}
+          onPress={(e) => e.stopPropagation()}
+        >
+          <CardBase
+            title={title}
+            subtitle={subtitle}
+            footer={footer}
+            scrollable={scrollable}
+            maxContentHeight={maxContentHeight}
+            borderWidth={0}
+            headerBorderWidth={3}
+            headerPadding={4}
+            contentPadding={4}
+            headerTextSize="text-lg"
+            contentBg={theme.primeBg}
+          >
+            {children}
+          </CardBase>
+        </Pressable>
+      </Pressable>
+    </Modal>
+  );
+};
+
+export default ModalBase;