✨ 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/package.json

@@ -16,6 +16,7 @@
 	},
 	"dependencies": {
 		"@manacore/shared-types": "workspace:*",
+		"@manacore/better-auth-types": "workspace:*",
 		"base64-js": "^1.5.1"
 	},
 	"devDependencies": {