桌面 GUI 外链修复 + 主题顺序调整（含结构扁平化进行中的工作区基线）

- 集成 tauri-plugin-opener：Cargo/lib.rs/capabilities/npm 四处接线，新增 src/openExternal.ts（桌面走 opener，浏览器回退 window.open，相对路径绝对化）
- 关于页 4 个链接、活动栏官网菜单、代理错误横幅 2 处健康检查链接全部改走 openExternal，桌面端可正常跳转
- 设置→外观 主题顺序调整为 深色/浅色/跟随系统
- release 二进制重编并验证（浏览器实测关于页链接可开文档页）
- 附带工作区中未提交的扁平化重构现状（另一会话进行中）
- homepage 落地页与文档终检通过（8787 / 与 /docs 双 200）

server/internal/proxy/handler.go

@@ -0,0 +1,116 @@
+package proxy
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+const maxResponseBytes = 10 << 20 // 10 MiB MVP safety cap
+
+type Handler struct {
+	BaseClient *http.Client
+}
+
+func NewHandler() *Handler {
+	return &Handler{BaseClient: &http.Client{Timeout: 30 * time.Second}}
+}
+
+func normalizeMethod(raw string) string {
+	m := strings.ToUpper(strings.TrimSpace(raw))
+	switch m {
+	case http.MethodGet, http.MethodPost, http.MethodPut, http.MethodPatch,
+		http.MethodDelete, http.MethodHead, http.MethodOptions:
+		return m
+	default:
+		return http.MethodGet
+	}
+}
+
+func (h *Handler) ProxyHTTP(c *gin.Context) {
+	var spec HttpSpec
+	if err := c.ShouldBindJSON(&spec); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid HttpSpec", "detail": err.Error()})
+		return
+	}
+
+	method := normalizeMethod(spec.Method)
+
+	u, err := ValidateURL(spec.URL)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+	query := u.Query()
+	for key, value := range spec.Query {
+		query.Set(key, value)
+	}
+	u.RawQuery = query.Encode()
+
+	var body io.Reader
+	if spec.Body != nil && spec.Body.Mode != "none" && method != http.MethodGet && method != http.MethodHead {
+		body = bytes.NewBufferString(spec.Body.Raw)
+	}
+
+	req, err := http.NewRequestWithContext(c.Request.Context(), method, u.String(), body)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "cannot create request", "detail": err.Error()})
+		return
+	}
+	for key, value := range spec.Headers {
+		// Hop-by-hop headers are managed by net/http.
+		if !isHopByHop(key) {
+			req.Header.Set(key, value)
+		}
+	}
+	if spec.Body != nil && spec.Body.Mode == "json" && req.Header.Get("Content-Type") == "" {
+		req.Header.Set("Content-Type", "application/json")
+	}
+
+	client := h.BaseClient
+	if spec.TimeoutMS > 0 {
+		client = &http.Client{Timeout: time.Duration(spec.TimeoutMS) * time.Millisecond}
+	}
+	started := time.Now()
+	res, err := client.Do(req)
+	if err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": "upstream request failed", "detail": err.Error()})
+		return
+	}
+	defer res.Body.Close()
+
+	payload, err := io.ReadAll(io.LimitReader(res.Body, maxResponseBytes+1))
+	if err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": "cannot read upstream response", "detail": err.Error()})
+		return
+	}
+	if len(payload) > maxResponseBytes {
+		c.JSON(http.StatusBadGateway, gin.H{"error": "upstream response exceeds 10 MiB limit"})
+		return
+	}
+
+	headers := make(map[string]string, len(res.Header))
+	for key, values := range res.Header {
+		headers[strings.ToLower(key)] = strings.Join(values, ", ")
+	}
+	c.JSON(http.StatusOK, HttpResult{
+		Status:  res.StatusCode,
+		Headers: headers,
+		Body:    string(payload),
+		TimeMS:  time.Since(started).Milliseconds(),
+		Size:    len(payload),
+	})
+}
+
+func isHopByHop(name string) bool {
+	switch strings.ToLower(name) {
+	case "connection", "keep-alive", "proxy-authenticate", "proxy-authorization", "te", "trailer", "transfer-encoding", "upgrade", "host", "content-length":
+		return true
+	default:
+		return false
+	}
+}