Add whitelist status API endpoints for early access key management

[Chucks1093]

Summary

Expose endpoints for checking whitelist status, fetching the full whitelist per key, and managing whitelist entries for creator-owned keys.

Scope

• GET /keys/:keyId/whitelist — full whitelist with date added per address
• GET /keys/:keyId/whitelist/:wallet — single wallet whitelist status
• POST /keys/:keyId/whitelist — add wallets (batch support up to 100)
• DELETE /keys/:keyId/whitelist/:wallet — remove wallet
• Whitelist gate status included in key detail API response

Acceptance Criteria

• Full whitelist returns all approved wallets with correct dates
• Single wallet check returns correct boolean status
• Batch add handles up to 100 wallets per request
• Remove endpoint restricted to key creator
• Gate status correctly reflected in key detail response

ETA

12 hours

[rupesh-kumar-sah]

Hello maintainers,

I would like to implement the whitelist status API endpoints for early access key management. My implementation roadmap:

1. REST Endpoint Handlers: Implement GET /keys/:keyId/whitelist (paginated full list), GET /keys/:keyId/whitelist/:wallet (boolean status query), POST /keys/:keyId/whitelist (batch addition up to 100 entries), and DELETE /keys/:keyId/whitelist/:wallet.
2. Access Control & Validation: Enforce creator authorization checks on mutation endpoints and validate Stellar wallet address formats.
3. Optimized Database Layer: Ensure database indexes on (key_id, wallet_address) for O(1) status queries and atomic batch operations.
4. Integration Test Suite: Write comprehensive integration tests covering batch addition, query validation, unauthorized access rejection, and address removal.

Looking forward to delivering a clean, production-ready implementation!