feat: resolve issues #209 #210 #211 #212

[Chuks-coderr]

Issue #212 — cache treasury balances endpoint

• Add in-memory 5-second TTL cache to GET /api/treasury/balances
• Invalidate cache immediately after execute-settlement succeeds
• Export getBalanceCache/setBalanceCache/invalidateBalanceCache for tests
• Add treasury-balances-cache.test.ts: cache helpers, TTL expiry, cache hit/miss on HTTP layer, invalidation after mutation

Issue #211 — integration tests for compliance allow/block endpoints

• Add compliance.test.ts with callComplianceOp unit tests: allow, block, allow_address_until, simulation error (422), send error (422), confirmation timeout (504)
• HTTP-layer tests for POST /compliance/allow and /compliance/block: 401 missing/wrong admin key, 400 invalid/missing address, 400 bad 'until' value, 503 missing env vars

Issue #210 — harden MongoDB connection error handling and pooling

• Add explicit pool config to MongoClient: maxPoolSize=10, minPoolSize=2, serverSelectionTimeoutMS=5000, connectTimeoutMS=10000, socketTimeoutMS=45000
• Wrap client.connect() in try/catch: MongoServerSelectionError produces a clear message with the URI and status 503
• Add 'error'/'close' event handlers to log topology failures
• Add _resetMongoSingleton() export for test isolation
• Add mongo-hardening.test.ts: 503 on unreachable host, URI in error message, non-selection error wrapping, success path, HTTP route returns 5xx on outage (not a hang)

Issue #209 — Redis reconnect backoff for event indexer

• Add createRedisClient() with ioredis retryStrategy implementing capped exponential backoff (base 250ms, cap 30s, ±10% jitter)
• Persist cursor to Redis (invoice_indexer_cursor) with in-memory fallback on Redis failure; loadCursor/saveCursor are safe to call while Redis is disconnected
• stopIndexer() gracefully quits the Redis connection
• startIndexer() accepts _redisClient injection for unit tests
• Add indexer-redis-reconnect.test.ts: backoffDelayMs range/growth/ cap, loadCursor fallback, saveCursor persistence and graceful failure, indexer continues polling after Redis drops

Closes #209
Closes #210
Closes #211
Closes #212

Pull Request

Summary

• Describe the purpose of this PR in one or two sentences.

Checklist

• Closes #__
• Tests added or updated
• ABI snapshot updated if contract sources changed (abis/ and COMEBACKHERE-contracts/)
• Screenshots attached if UI changed
• Documentation updated if needed

Notes

• For contract changes, verify ABI snapshot hygiene with make check-abi-snapshots.
• For UI changes, include screenshots or screen recordings to help reviewers.
  closes
  closes Add Redis reconnection/backoff handling to the event indexer #209
  closes Add MongoDB connection error handling and pooling config #210
  closes Add integration tests for compliance allow/block endpoints #211
  closes Add caching to GET /api/treasury/balances #212

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