Test/paginated response

[motchiy-tuti]

What does this PR do?

Adds dedicated unit tests for PaginatedResponse<T> parsing edge cases (test/shared/models/paginated_response_test.dart) and enhances PaginatedResponse with robust page, hasMore, and toJson serialization support.

• Covers fromJson with non-empty page and empty items list.
• Handles missing or null page / hasMore fields with safe default fallbacks.
• Adds toJson() round-trip verification.

Type of change

• feat — new feature for template users
• fix — bug in the template
• docs — documentation only
• refactor — refactoring without behavior change
• test — adding/fixing tests
• chore — CI, deps, tooling

Checklist

• flutter analyze lib/ test/ --fatal-infos — 0 issues
• dart format --set-exit-if-changed . — no diff
• flutter test — all tests pass
• Tests added for new logic (domain layer required)
• Documentation updated (README, ARCHITECTURE.md, CHANGELOG.md if needed)
• No hardcoded secrets / API keys / domains
• Clean Architecture Dependency Rule NOT violated (domain does not depend on data/presentation)
• New dependency? Updated Stack table in README/ARCHITECTURE + pubspec.yaml

Notes for reviewers

All verification checks (flutter analyze, flutter test, and tool/check_boundaries.dart) passed successfully without any issues.