✨ feat(auth): add centralized @manacore/better-auth-types package

Create new shared package for Better Auth type definitions:
- UserRole, JWTPayload, CurrentUserData types
- Type guards: isValidUserRole, isValidOrganizationRole
- Utility functions: jwtPayloadToCurrentUser
- userAdditionalFields for client type inference

Migrate shared packages to use centralized types:
- @manacore/shared-auth re-exports from new package
- @manacore/shared-nestjs-auth uses new package as dependency

packages/shared-auth/src/better-auth-fields.ts

@@ -0,0 +1,35 @@
+/**
+ * Better Auth Additional Field Definitions
+ *
+ * Re-exports centralized types from @manacore/better-auth-types.
+ * This file is provided for convenience when importing from @manacore/shared-auth.
+ *
+ * @example
+ * ```typescript
+ * // In SvelteKit/React app
+ * import { createAuthClient } from "better-auth/client";
+ * import { inferAdditionalFields } from "better-auth/client/plugins";
+ * import { userAdditionalFields } from "@manacore/shared-auth";
+ *
+ * export const authClient = createAuthClient({
+ *   baseURL: "http://localhost:3001",
+ *   plugins: [inferAdditionalFields(userAdditionalFields)],
+ * });
+ *
+ * // Now user.role is properly typed!
+ * const session = await authClient.getSession();
+ * console.log(session?.user.role); // TypeScript knows this is string
+ * ```
+ *
+ * @see https://www.better-auth.com/docs/concepts/typescript
+ */
+
+// Re-export from centralized package
+export {
+	userAdditionalFields,
+	type UserRole,
+	type OrganizationRole,
+	type UserWithAdditionalFields,
+	isValidUserRole,
+	isValidOrganizationRole,
+} from '@manacore/better-auth-types';

packages/shared-auth/src/index.ts

@@ -1,6 +1,16 @@
 // Types
 export * from './types';
 
+// Better Auth field definitions for client type inference
+export {
+	userAdditionalFields,
+	type UserRole,
+	type OrganizationRole,
+	type UserWithAdditionalFields,
+	isValidUserRole,
+	isValidOrganizationRole,
+} from './better-auth-fields';
+
 // Core utilities
 import { createAuthService as _createAuthService } from './core/authService';
 export { createAuthService } from './core/authService';