refactor(edge): 抽取边缘运行时共享包并完成 Phase 3 重构

- 新增 internal/apps/edge/，三组件改为薄包装，删除 3000+ 行重复代码
- Agent 心跳周期下沉至 heartbeat/cycle.go
- 协议类型迁入 pkg/protocol/agent.go
- 补充设计文档与 changelog

internal/apps/edge/httpclient/client.go

@@ -0,0 +1,132 @@
+package httpclient
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"log/slog"
+	"net/http"
+	"strings"
+	"time"
+)
+
+type Client struct {
+	baseURL    string
+	token      string
+	authHeader string
+	httpClient *http.Client
+}
+
+func New(baseURL, token string, timeout time.Duration, authHeader string) *Client {
+	return &Client{
+		baseURL:    strings.TrimRight(baseURL, "/"),
+		token:      token,
+		authHeader: authHeader,
+		httpClient: &http.Client{Timeout: timeout},
+	}
+}
+
+func (c *Client) SetToken(token string) {
+	c.token = strings.TrimSpace(token)
+	slog.Debug("http client token updated")
+}
+
+func (c *Client) GetJSON(ctx context.Context, path string, target any) error {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+path, nil)
+	if err != nil {
+		return err
+	}
+	c.setAuthHeader(req)
+	return c.do(req, target)
+}
+
+func (c *Client) PostJSON(ctx context.Context, path string, body any, target any) error {
+	data, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+path, bytes.NewReader(data))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	c.setAuthHeader(req)
+	return c.do(req, target)
+}
+
+func (c *Client) DoRaw(ctx context.Context, method, path string, headers map[string]string) (*http.Response, error) {
+	req, err := http.NewRequestWithContext(ctx, method, c.baseURL+path, nil)
+	if err != nil {
+		return nil, err
+	}
+	c.setAuthHeader(req)
+	for key, value := range headers {
+		req.Header.Set(key, value)
+	}
+	return c.httpClient.Do(req)
+}
+
+func (c *Client) setAuthHeader(req *http.Request) {
+	if c.authHeader != "" {
+		req.Header.Set(c.authHeader, c.token)
+	}
+}
+
+func (c *Client) do(req *http.Request, target any) error {
+	res, err := c.httpClient.Do(req)
+	if err != nil {
+		slog.Error("http request failed", "method", req.Method, "path", req.URL.Path, "error", err)
+		return err
+	}
+	defer func(Body io.ReadCloser) {
+		err := Body.Close()
+		if err != nil {
+			slog.Error("failed to close response body", "error", err)
+		}
+	}(res.Body)
+
+	body, err := io.ReadAll(res.Body)
+	if err != nil {
+		slog.Error("http response read failed", "method", req.Method, "path", req.URL.Path, "error", err)
+		return err
+	}
+	if res.StatusCode != http.StatusOK {
+		slog.Warn("http request returned non-200", "method", req.Method, "path", req.URL.Path, "status", res.Status)
+		return ReadBodyError(body, res.Status)
+	}
+	if target == nil {
+		return nil
+	}
+	if err = json.Unmarshal(body, target); err != nil {
+		slog.Error("http response decode failed", "method", req.Method, "path", req.URL.Path, "error", err)
+		return err
+	}
+	return nil
+}
+
+func APIError(msg string) error {
+	if strings.TrimSpace(msg) == "" {
+		return nil
+	}
+	return errors.New(msg)
+}
+
+func ReadBodyError(body []byte, fallback string) error {
+	var errBody struct {
+		ErrorMsg string `json:"error_msg"`
+	}
+	if err := json.Unmarshal(body, &errBody); err == nil && strings.TrimSpace(errBody.ErrorMsg) != "" {
+		return errors.New(errBody.ErrorMsg)
+	}
+	return errors.New(fallback)
+}
+
+func ReadHTTPError(res *http.Response) error {
+	body, err := io.ReadAll(res.Body)
+	if err != nil {
+		return errors.New(res.Status)
+	}
+	return ReadBodyError(body, res.Status)
+}