fix(settlement): verify on-chain broadcast confirmation before marking claims settled

[trexfr-ops]

Summary

Closes #8230

This PR addresses the false-success pathways in sign_and_broadcast_transaction() where claims could transition to settled with a synthetic hash when no broadcast to the network occurred.

Changes

1. Require TREASURY_KEY_PATH and NODE_API_URL configuration; returns (False, None, error_message) if unset.
2. Require confirmed HTTP 2xx response from /api/tx/submit before returning success=True and on_chain_hash.
3. Handle non-2xx broadcast responses and network errors by returning success=False with error details, allowing process_claims_batch() to release pool funds and retain claims for retry.
4. Updated TestSignAndBroadcastTransaction suite covering missing configuration, signing errors, broadcast failures, and verified 2xx success (100% pass).

Bounty Payout Addresses

• EVM (Base/ETH): 0x32BB3df5B74a594956a0f33Bc353511Fa759FCa4
• Solana (SOL): 8Xo39uq9LoaM2rQEkgaaSfuThqHZTd18yGdJSXffkLwM
• LTC: LPnftYop8yhRNQZstysT3vuJf3XkpQWKTC
• BTC: bc1qpyu6866qcgt26sqw4dn2mlmp8d0yc657fuedkv
• DOGE: DDMU6D9TCE3BhqqYyy7MUZQD7JhfL39FpE

[github-actions]

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