[ocakciomursel-pixel]

Closes #42

Summary

Adds sigma-rust (ergo-lib) local wallet support so that the chaincash server can derive keys, select unspent boxes, and sign transactions locally without requiring an unlocked node wallet:

• LocalWallet & WalletConfig (crates/chaincash_services/src/wallet.rs):
  • Supports configuring a BIP-39 mnemonic (with optional mnemonic_password and derivation_paths, defaulting to m/44'/429'/0'/0/0) and/or raw base16 DlogProverInput secrets in [wallet].
  • Derives P2PK addresses and EcPoint public keys locally.
  • Fetches unspent boxes by address via the node's /blockchain/box/unspent/byAddress indexer endpoint (node.endpoints().blockchain()?.unspent_by_address(...)).
  • Builds ErgoStateContext from the latest 10 block headers via /blocks/chainSlice, signs UnsignedTransaction locally using ergo_lib::wallet::Wallet::sign_transaction + TransactionContext, and submits signed transactions via POST /transactions.
• TransactionService & ServerState (crates/chaincash_services/src/{lib,transaction,scanner}.rs):
  • Uses LocalWallet for wallet_pubkeys, get_utxos, box_selection_with_amount, get_tx_ctx, get_private_key, and sign_and_submit across mint_reserve, top_up_reserve, mint_note, spend_note, and redeem_note when configured, while preserving full backward compatibility with the node wallet when [wallet] is not configured.
  • Updates wait_scan_block in scanner.rs to poll /blockchain/indexedHeight instead of /wallet/status when LocalWallet is active.
• Tests:
  • Added unit tests for BIP-39 mnemonic + secret key derivation and local sigma-rust signing of reserve mint & top-up transactions.