feat: Circuit integrity, wallet monitor, XDR decoder & tx monitor

[Dev-sandy1]

Summary

Implements features for issues #1061, #1062, #1063, and #1077:

Issue #1077 — Circuit Verification Key Integrity Manifest & Boot-Time Attestation

• Added \CircuitIntegrityVerifier\ class in \zk-proof-service/lib/circuit-integrity.js\
• Maintains HMAC-signed \manifest.json\ with SHA-256 hashes of all circuit artifacts
• Verifies all circuit file checksums against manifest during server boot
• Refuses service startup if any artifact fails checksum attestation
• Integrated into \createServer()\ in \zk-proof-service/server.js\

Issue #1063 — Wallet Balance Low-Threshold Monitor & Auto-Refill Sweep Alerts

• Added \WalletBalanceMonitor\ class in \keeper/src/walletBalanceMonitor.js\
• Monitors keeper XLM balance every 60 seconds (configurable)
• Multi-channel alerts: PagerDuty, Discord, Telegram
• Warning threshold (default 50 XLM) and critical threshold (default 20 XLM)
• Automated XLM sweep from funding wallet when below critical threshold
• Added config options in \keeper/src/config.js\

Issue #1062 — Stellar XDR Structured Error Decoder & Automated Recovery Engine

• Added \XDRErrorDecoder\ class in \keeper/src/xdrErrorDecoder.js\
• Decodes base64 XDR error strings using @stellar/stellar-sdk\
• Maps result codes to automated recovery actions:
  • \ xBAD_SEQ\ → Resync sequence counter
  • \ xINSUFFICIENT_FEE\ → Escalate fee and retry
  • \HostError\ → Quarantine task to DLQ
  • \ xBAD_AUTH\ → Alert operator
  • \ xINSUFFICIENT_BALANCE\ → Top up wallet
• Injectable recovery handlers for custom deployment logic

Issue #1061 — Durable Transaction Monitor & Unconfirmed Timeout Resolution

• Added \TxMonitor\ class in \keeper/src/txMonitor.js\
• Persists submitted transaction hashes with persistence adapters (Memory/Redis)
• Background worker polls \getTransaction\ until terminal state or expiry
• Configurable max ledger age (default 10 ledgers) before expiry
• Emits status change events: \ xConfirmed, \ xFailed, \ xExpired, \ xStatusChange\
• Resilient across keeper crashes via persistent store

Testing

All new modules are designed with injectable dependencies for testability:

• \WalletBalanceMonitor: inject custom \getBalanceFn, \sendAlertFn, \sweepFn\
• \XDRErrorDecoder: inject recovery handlers via constructor
• \TxMonitor: inject custom store adapter and logger
• \CircuitIntegrityVerifier: inject custom logger and signing secret

Closes #1061
Closes #1062
Closes #1063
Closes #1077

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Pr Under Review.