Add Support for 'Platform-wide' Token Airdrops

### Context
Rewarding loyal community members.

### Problem
Airdropping tokens to 10k users manualy is error-prone.

### Suggested Execution
- Build an 'AirdropManager'.
- Iterates over 'ReputationToken' holders and queues batch transfers.

### Acceptance Criteria
- Efficient community rewards.
- Robust tracking and verification.

### References
- backend/src/marketing/airdrop.service.ts