feat: 블록체인(chain) 통합 및 내부 API 추가

- internal/chain 패키지 추가 (client, handler, service, repository, model)
- 체인 연동 엔드포인트: 지갑 조회, 잔액, 자산, 인벤토리, 마켓 등
- 관리자 전용 체인 엔드포인트: 민팅, 보상, 템플릿 등록
- 게임 서버용 내부 API (/api/internal/chain/*) + ServerAuth 미들웨어
- 회원가입 시 블록체인 월렛 자동 생성
- 체인 관련 환경변수 및 InternalAPIKey 설정 추가

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/chain/client.go

@@ -0,0 +1,145 @@
+package chain
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"sync/atomic"
+	"time"
+)
+
+type rpcRequest struct {
+	JSONRPC string `json:"jsonrpc"`
+	ID      int64  `json:"id"`
+	Method  string `json:"method"`
+	Params  any    `json:"params"`
+}
+
+type rpcResponse struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      any             `json:"id"`
+	Result  json.RawMessage `json:"result,omitempty"`
+	Error   *rpcError       `json:"error,omitempty"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+func (e *rpcError) Error() string {
+	return fmt.Sprintf("RPC error %d: %s", e.Code, e.Message)
+}
+
+// Client is a JSON-RPC 2.0 client for the TOL Chain node.
+type Client struct {
+	nodeURL string
+	http    *http.Client
+	idSeq   atomic.Int64
+}
+
+func NewClient(nodeURL string) *Client {
+	return &Client{
+		nodeURL: nodeURL,
+		http:    &http.Client{Timeout: 10 * time.Second},
+	}
+}
+
+// Call invokes a JSON-RPC method and unmarshals the result into out.
+func (c *Client) Call(method string, params any, out any) error {
+	reqBody := rpcRequest{
+		JSONRPC: "2.0",
+		ID:      c.idSeq.Add(1),
+		Method:  method,
+		Params:  params,
+	}
+	data, err := json.Marshal(reqBody)
+	if err != nil {
+		return fmt.Errorf("marshal RPC request: %w", err)
+	}
+
+	resp, err := c.http.Post(c.nodeURL, "application/json", bytes.NewReader(data))
+	if err != nil {
+		return fmt.Errorf("RPC network error: %w", err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return fmt.Errorf("read RPC response: %w", err)
+	}
+
+	var rpcResp rpcResponse
+	if err := json.Unmarshal(body, &rpcResp); err != nil {
+		return fmt.Errorf("unmarshal RPC response: %w", err)
+	}
+	if rpcResp.Error != nil {
+		return rpcResp.Error
+	}
+	if out != nil {
+		if err := json.Unmarshal(rpcResp.Result, out); err != nil {
+			return fmt.Errorf("unmarshal RPC result: %w", err)
+		}
+	}
+	return nil
+}
+
+// --- Typed convenience methods ---
+
+type BalanceResult struct {
+	Address string `json:"address"`
+	Balance uint64 `json:"balance"`
+	Nonce   uint64 `json:"nonce"`
+}
+
+func (c *Client) GetBalance(address string) (*BalanceResult, error) {
+	var result BalanceResult
+	err := c.Call("getBalance", map[string]string{"address": address}, &result)
+	return &result, err
+}
+
+func (c *Client) GetAsset(id string) (json.RawMessage, error) {
+	var result json.RawMessage
+	err := c.Call("getAsset", map[string]string{"id": id}, &result)
+	return result, err
+}
+
+func (c *Client) GetAssetsByOwner(owner string, offset, limit int) (json.RawMessage, error) {
+	var result json.RawMessage
+	err := c.Call("getAssetsByOwner", map[string]any{
+		"owner": owner, "offset": offset, "limit": limit,
+	}, &result)
+	return result, err
+}
+
+func (c *Client) GetInventory(owner string) (json.RawMessage, error) {
+	var result json.RawMessage
+	err := c.Call("getInventory", map[string]string{"owner": owner}, &result)
+	return result, err
+}
+
+func (c *Client) GetActiveListings(offset, limit int) (json.RawMessage, error) {
+	var result json.RawMessage
+	err := c.Call("getActiveListings", map[string]any{
+		"offset": offset, "limit": limit,
+	}, &result)
+	return result, err
+}
+
+func (c *Client) GetListing(id string) (json.RawMessage, error) {
+	var result json.RawMessage
+	err := c.Call("getListing", map[string]string{"id": id}, &result)
+	return result, err
+}
+
+type SendTxResult struct {
+	TxID string `json:"tx_id"`
+}
+
+func (c *Client) SendTx(tx any) (*SendTxResult, error) {
+	var result SendTxResult
+	err := c.Call("sendTx", tx, &result)
+	return &result, err
+}