feat(pay): Phase D 归集 —— 气隙签名 sweep(#34/34A)

动钱代码,按"联网建/广播 + 离线签"气隙流程,离线签名独立验签防篡改:
- wallet: DecodeTronAddress/TronAddressBodyHex(base58check 解码校验)、AddressFromMnemonic(离线校验用)。
- tron/sign: TxID(sha256 raw_data)、SignRawData(secp256k1 → R||S||recid 65B)、RecoverAddressBody。
- tron/abi: ABIEncodeTransferParams(transfer(address,uint256) 参数)、keccak 地址体。
- tron/tx(联网): BuildTransfer(triggersmartcontract 建未签名)、TRC20Balance、Broadcast。
- cmd/sweep: plan/build/sign/broadcast 四段;sign 对每笔独立验:①重算 txid 防篡改 ②收款人+额 ABI
  内嵌 ③USDT 合约内嵌 ④派生地址==owner,任一不符拒签;助记词只经 PAY_SWEEP_MNEMONIC(离线机,不入 arg)。
- 测试:签名可恢复到正确地址、ABI 编码、地址解码 roundtrip 全绿。
- 联网上链部分标注需 Phase E 真链验证;README 补 sweep 用法 + 验签说明 + gas 提醒。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pay/internal/tron/abi.go

@@ -0,0 +1,41 @@
+package tron
+
+import (
+	"encoding/hex"
+	"fmt"
+	"math/big"
+
+	"github.com/wangjia/pangolin/pay/internal/wallet"
+	"golang.org/x/crypto/sha3"
+)
+
+// TransferSelector is the TRC20 transfer(address,uint256) function selector
+// string that TronGrid's triggersmartcontract expects.
+const TransferSelector = "transfer(address,uint256)"
+
+// ABIEncodeTransferParams builds the 64-byte ABI parameter for
+// transfer(address,uint256): the recipient (20-byte body, left-padded to 32) and
+// the amount (uint256, left-padded to 32). Returns hex (no 0x, no 4-byte
+// selector — TronGrid derives the selector from TransferSelector).
+func ABIEncodeTransferParams(toAddr string, amount int64) (string, error) {
+	if amount <= 0 {
+		return "", fmt.Errorf("tron: transfer amount must be positive")
+	}
+	payload, err := wallet.DecodeTronAddress(toAddr)
+	if err != nil {
+		return "", err
+	}
+	out := make([]byte, 64)
+	copy(out[12:32], payload[1:]) // 20-byte body, right-aligned in first word
+	new(big.Int).SetInt64(amount).FillBytes(out[32:64])
+	return hex.EncodeToString(out), nil
+}
+
+// keccakAddressBody derives the 20-byte address body from a 65-byte uncompressed
+// secp256k1 public key: keccak256(X||Y)[12:].
+func keccakAddressBody(uncompressed []byte) []byte {
+	h := sha3.NewLegacyKeccak256()
+	h.Write(uncompressed[1:])
+	sum := h.Sum(nil)
+	return sum[12:]
+}