feat(keys): add auction, metadata & staking endpoints; extend holders with staked/liquid quantities

[devJaja]

Closes #844
Closes #845
Closes #846
Closes #847

Summary

This PR adds four key-related endpoints and extends the holders endpoint with staking data.

#844 — Auction state endpoint

• GET /api/v1/keys/:keyId/auction (no auth)
• Returns auctionPrice, auctionSupply, auctionSold, and auctionStatus (not_configured | active | completed)
• Reads auction state from persistent contract storage via Soroban RPC
• 30s Redis cache; invalidated after each auction buy
• 404 for unknown key IDs

#845 — Key metadata endpoint

• GET /api/v1/keys/:keyId/metadata (no auth)
• Returns name, bio, avatarUri, and creatorAddress from on-chain storage via Soroban RPC
• 5-minute Redis cache; invalidated on metadata_updated events
• 404 when no metadata has been initialised or for unknown key IDs

#846 — Holder registry with staked/liquid balance

• Extends GET /api/v1/creators/:id/holders with stakedQuantity and liquidQuantity per holder
• liquidQuantity = key_balance - stakedQuantity
• Staking positions read from the staking_positions persistent map, each holder cached in Redis for 30s
• Backward compatible — existing fields unchanged

#847 — Staking pool stats endpoint

• GET /api/v1/keys/:keyId/staking (no auth)
• Returns stakingPoolBalance, totalStaked, recentFeeInflow (sum of fees in the past 30 days), and stakerCount
• Read from on-chain contract storage via Soroban RPC
• 60s Redis cache; invalidated on stake, unstake, or fee collection events
• 404 for unknown key IDs

Tests

Added unit tests for all new services. Build and lint pass.

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[Chucks1093]

❌ CI Failed — verify (Server CI)

The verify check is failing on this PR.

Likely causes:

• TypeScript compile error from a type mismatch or missing property
• Test is failing due to a mock not being set up for the new service method
• ESLint rule violation (e.g., no-explicit-any, no-unused-vars)

Steps to fix:

1. Run npm run build locally and fix all TypeScript errors
2. Run npm test and fix any failing tests
3. Run npm run lint to catch ESLint issues
4. Push