fix: use explicit SQL UPDATE for balance changes and add value field mapping

Changed transaction failure logging from error to warning level in PoA proposer.
Removed immediate session.commit() after state transition as balance changes are now persisted via explicit SQL UPDATE statements.
Added "value" field mapping from "amount" in transaction normalization and PoA proposer to ensure state transition compatibility.
Replaced SQLAlchemy ORM balance updates with explicit SQL UPDATE statements using

apps/blockchain-node/src/aitbc_chain/consensus/poa.py

@@ -278,18 +278,16 @@ class PoAProposer:
                     # Use original tx_data from mempool to preserve type and payload
                     tx_data_for_transition = tx.content.copy()
                     tx_data_for_transition["nonce"] = sender_account.nonce
+                    # Map "amount" to "value" for state transition compatibility
+                    tx_data_for_transition["value"] = tx_data_for_transition.get("amount", 0)
                     success, error_msg = state_transition.apply_transaction(
                         session, self._config.chain_id, tx_data_for_transition, tx.tx_hash
                     )
                     
                     if not success:
-                        self._logger.error(f"[PROPOSE] Failed to apply transaction {tx.tx_hash}: {error_msg}")
+                        self._logger.warning(f"[PROPOSE] Failed to apply transaction {tx.tx_hash}: {error_msg}")
                         continue
 
-                    # Commit the balance changes immediately after successful state transition
-                    session.commit()
-                    self._logger.info(f"[PROPOSE] Committed balance changes for tx {tx.tx_hash}")
-
                     # Check if transaction already exists in database
                     existing_tx = session.exec(
                         select(Transaction).where(