Implement Mihomo external-controller support in configuration and gateway

- Added optional Mihomo configuration fields in `config.compose.yaml` and `config.example.yaml` for enhanced integration with the Mihomo external-controller.
- Updated the `Gateway` to handle Mihomo API requests, including proxying and error handling for Mihomo-specific endpoints.
- Enhanced the documentation in `GATEWAY_RUN.md` to guide users on configuring Mihomo integration.
- Introduced new utility functions in the web client for interacting with Mihomo API endpoints, improving the overall user experience.
- Updated the sidebar in the Svelte components to include a link to the Mihomo section, enhancing navigation.

internal/proxy/mihomo.go

@@ -0,0 +1,73 @@
+package proxy
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"strings"
+)
+
+// NewMihomoForward proxies /api/{alias}/mihomo/... to Mihomo external-controller (REST + WebSocket).
+func NewMihomoForward(
+	target *url.URL,
+	stripPrefix string,
+	auth string,
+	rt http.RoundTripper,
+	errHandler func(http.ResponseWriter, *http.Request, error),
+) http.Handler {
+	if errHandler == nil {
+		errHandler = defaultForwardErrorHandler
+	}
+	if rt == nil {
+		rt = http.DefaultTransport
+	}
+	rp := &httputil.ReverseProxy{
+		Director: func(req *http.Request) {
+			NormalizeRequestURLPath(req)
+			p := req.URL.Path
+			if !strings.HasPrefix(p, stripPrefix) {
+				return
+			}
+			rest := strings.TrimPrefix(p, stripPrefix)
+			rest = strings.TrimPrefix(rest, "/")
+			q := req.URL.RawQuery
+			dest := JoinPathPrefix(target, "/", rest)
+			req.URL.Scheme = dest.Scheme
+			req.URL.Host = dest.Host
+			req.URL.Path = dest.Path
+			req.URL.RawQuery = q
+			req.Host = dest.Host
+			req.Header.Del("Authorization")
+			if auth != "" {
+				req.Header.Set("Authorization", auth)
+			}
+		},
+		Transport: rt,
+		ErrorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
+			errHandler(w, r, err)
+		},
+	}
+	return rp
+}
+
+// MihomoMetaJSON returns a JSON body for GET .../mihomo/meta (display URL without credentials).
+func MihomoMetaJSON(target *url.URL) []byte {
+	display := strings.TrimSuffix(target.String(), "/")
+	b, _ := json.Marshal(map[string]any{
+		"ok":              true,
+		"controller_base": display,
+	})
+	return b
+}
+
+// MihomoJSONError writes a JSON error for Mihomo routes when proxy is not configured.
+func MihomoJSONError(w http.ResponseWriter, code, msg string) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(http.StatusNotFound)
+	_ = json.NewEncoder(w).Encode(map[string]any{
+		"ok":    false,
+		"error": map[string]string{"code": code, "message": msg},
+	})
+}
+

internal/proxy/mihomo_test.go

@@ -0,0 +1,37 @@
+package proxy
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+)
+
+func TestMihomoForwardRewritesPathAndAuth(t *testing.T) {
+	target, err := url.Parse("http://127.0.0.1:9090")
+	if err != nil {
+		t.Fatal(err)
+	}
+	cap := &captureTransport{}
+	h := NewMihomoForward(target, "/api/mtg/mihomo", "Bearer testsecret", cap, nil)
+
+	req, err := http.NewRequestWithContext(context.Background(), http.MethodGet, "http://gw/api/mtg/mihomo/proxies", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Header.Set("Authorization", "Bearer client-should-not-forward")
+	h.ServeHTTP(httptest.NewRecorder(), req)
+
+	if cap.got == nil {
+		t.Fatal("no outgoing request captured")
+	}
+	if got := cap.got.Header.Get("Authorization"); got != "Bearer testsecret" {
+		t.Fatalf("Authorization: got %q want Bearer testsecret", got)
+	}
+	want, err := url.Parse("http://127.0.0.1:9090/proxies")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertSameURL(t, cap.got.URL, want)
+}