fix: export missing hooks and types from @soroban/abacus-react package

- Export useAbacusConfig and useAbacusDisplay hooks from AbacusContext
- Export getDefaultAbacusConfig function and AbacusDisplayProvider component
- Export ColorScheme, BeadShape, ColorPalette, AbacusDisplayConfig, and AbacusDisplayContextType types

Resolves import errors in web components that were trying to import these
hooks but they weren't being exported from the package's main index file.

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

Co-Authored-By: Claude <noreply@anthropic.com>

packages/abacus-react/src/index.ts

@@ -3,4 +3,18 @@ export type {
   AbacusConfig,
   BeadConfig,
   AbacusDimensions
-} from './AbacusReact';
+} from './AbacusReact';
+
+export {
+  useAbacusConfig,
+  useAbacusDisplay,
+  getDefaultAbacusConfig,
+  AbacusDisplayProvider
+} from './AbacusContext';
+export type {
+  ColorScheme,
+  BeadShape,
+  ColorPalette,
+  AbacusDisplayConfig,
+  AbacusDisplayContextType
+} from './AbacusContext';