Add Admin Role Separation

[MaryammAli]

This PR introduces a structured role-based administration system to improve governance, scalability, and long-term maintainability of the quest contract.

Previously, all privileged operations were centralized under a single owner account. While functional for smaller deployments, this approach becomes increasingly restrictive and difficult to manage as the platform grows and more contributors need operational access. It also creates unnecessary dependency on a single administrator for routine quest management tasks.

To address this, the contract now supports additional manager/moderator roles alongside the owner role. These managers are granted limited administrative capabilities focused specifically on quest operations, allowing them to create, update, and manage quests without receiving full ownership privileges over the contract.

The owner role remains the highest authority within the system and retains exclusive control over governance-sensitive actions such as assigning or revoking manager permissions. This ensures delegation can happen safely without compromising security or ownership integrity.

This separation of responsibilities provides several important improvements:

• Better scalability for multi-admin environments
• Safer delegation of operational tasks
• Reduced administrative bottlenecks
• Improved governance and permission control
• Clearer separation between platform ownership and day-to-day management
• Stronger foundation for future expansion of access-control features

The implementation also improves maintainability by creating a cleaner authorization structure that can be extended more easily in future updates if additional roles or permissions are introduced.

Testing was performed to verify:

• Managers can successfully create and manage quests
• Unauthorized users cannot access restricted functions
• Only the owner can assign or revoke manager roles
• Existing owner permissions remain fully intact
• Permission boundaries behave correctly across all role checks

Overall, this update establishes a more flexible and production-ready administrative model for the platform while preserving strong security guarantees around ownership and governance.
Closes #207

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