feat: persist draft messages and UI refinements

- Add dedicated draft-store with AsyncStorage persistence for drafts
  that survive app refresh/crash
- Reduce markdown bold weight from bold to medium (500)
- Various theme and component style updates
- Server bootstrap and config improvements

🤖 Generated with [Claude Code](https://claude.com/claude-code)

packages/app/src/components/file-drop-zone.tsx

@@ -80,7 +80,7 @@ const styles = StyleSheet.create((theme) => ({
   },
   backdrop: {
     ...StyleSheet.absoluteFillObject,
-    backgroundColor: theme.colors.background,
+    backgroundColor: theme.colors.surface0,
     opacity: 0.7,
   },
   overlayContent: {