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/app/(tabs)/chat.tsx

@@ -114,9 +114,7 @@ const Chat = () => {
     const message = messages.find((m) => m.id === messageId);
     if (message?.proposedChanges) {
       const updatedProposals = message.proposedChanges.map((p) =>
-        p.id === proposalId
-          ? { ...p, respondedAction: action }
-          : p,
+        p.id === proposalId ? { ...p, respondedAction: action } : p,
       );
       updateMessage(messageId, { proposedChanges: updatedProposals });
     }