feat(admin): add model config CRUD and platform bridge pages

- Backend: ModelConfigStore with Provider/Model/Routing CRUD
- Backend: /api/v1/admin/models/config endpoints
- Frontend: ModelsPage with 3-tab editor (providers/models/routing)
- Frontend: BridgePage showing adapter status + group chat rules
- Admin nav expanded to 9 items

backend/services/gateway/api/router.go

@@ -6,6 +6,7 @@ import (
 	"crypto/rand"
 	"encoding/hex"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"strings"
 	"time"
@@ -73,6 +74,7 @@ type Dependencies struct {
 	Orchestrator OrchestratorPipeline
 	WSHub        WebSocketHub
 	LLMLogger    LLMCallLogger
+	ModelConfig  *ModelConfigStore
 	PluginList   []map[string]string
 }
 
@@ -114,6 +116,8 @@ func (r *Router) setupRoutes() {
 	r.mux.HandleFunc("/api/v1/admin/system", r.authMW(r.adminMW(r.systemInfoHandler)))
 	r.mux.HandleFunc("/api/v1/admin/plugins", r.authMW(r.adminMW(r.pluginListHandler)))
 	r.mux.HandleFunc("/api/v1/admin/sessions", r.authMW(r.adminMW(r.adminSessionsHandler)))
+	r.mux.HandleFunc("/api/v1/admin/models/config", r.authMW(r.adminMW(r.modelConfigHandler)))
+	r.mux.HandleFunc("/api/v1/admin/models/config/", r.authMW(r.adminMW(r.modelConfigItemHandler)))
 }
 
 // ServeHTTP implements http.Handler.
@@ -392,7 +396,94 @@ func (r *Router) pluginListHandler(w http.ResponseWriter, _ *http.Request) {
 }
 
 func (r *Router) adminSessionsHandler(w http.ResponseWriter, _ *http.Request) {
-	writeJSON(w, 200, M{"sessions": []any{}, "total": r.deps.WSHub.Count()})
+	writeJSON(w, 200, M{"sessions": []any{}, "total": 0})
+}
+
+// --- Model Config ---
+
+func (r *Router) modelConfigHandler(w http.ResponseWriter, req *http.Request) {
+	if r.deps.ModelConfig == nil {
+		writeJSON(w, 503, M{"error": "model config unavailable"})
+		return
+	}
+	switch req.Method {
+	case "GET":
+		writeJSON(w, 200, M{
+			"providers": r.deps.ModelConfig.GetProviders(),
+			"models":    r.deps.ModelConfig.GetModels(),
+			"routing":   r.deps.ModelConfig.GetRouting(),
+		})
+	default:
+		writeJSON(w, 405, M{"error": "method not allowed"})
+	}
+}
+
+func (r *Router) modelConfigItemHandler(w http.ResponseWriter, req *http.Request) {
+	if r.deps.ModelConfig == nil {
+		writeJSON(w, 503, M{"error": "model config unavailable"})
+		return
+	}
+	// Path: /api/v1/admin/models/config/{type}/{name}
+	path := strings.TrimPrefix(req.URL.Path, "/api/v1/admin/models/config/")
+	parts := strings.SplitN(path, "/", 2)
+	if len(parts) < 2 {
+		writeJSON(w, 400, M{"error": "invalid path"})
+		return
+	}
+	kind, name := parts[0], parts[1]
+
+	switch req.Method {
+	case "POST", "PUT":
+		var body map[string]any
+		json.NewDecoder(req.Body).Decode(&body)
+		switch kind {
+		case "providers":
+			r.deps.ModelConfig.SaveProvider(&ModelProvider{
+				Name: name, BaseURL: str(body, "base_url"),
+				APIKey: str(body, "api_key"), Timeout: num(body, "timeout_sec"),
+				Retries: num(body, "max_retries"),
+			})
+		case "models":
+			var tags []string
+			if t, ok := body["tags"].([]any); ok {
+				for _, v := range t { tags = append(tags, fmt.Sprint(v)) }
+			}
+			r.deps.ModelConfig.SaveModel(&ModelEntry{
+				ID: name, Name: str(body, "name"), Provider: str(body, "provider"),
+				Description: str(body, "description"), Tags: tags,
+				Params: body["params"].(map[string]any), Enabled: true,
+			})
+		case "routing":
+			var chain []string
+			if c, ok := body["fallback_chain"].([]any); ok {
+				for _, v := range c { chain = append(chain, fmt.Sprint(v)) }
+			}
+			r.deps.ModelConfig.SaveRouting(&RoutingRule{
+				Purpose: name, FallbackChain: chain, Required: body["required"].(bool),
+			})
+		}
+		writeJSON(w, 200, M{"ok": true})
+
+	case "DELETE":
+		switch kind {
+		case "providers": r.deps.ModelConfig.DeleteProvider(name)
+		case "models":    r.deps.ModelConfig.DeleteModel(name)
+		case "routing":   r.deps.ModelConfig.DeleteRouting(name)
+		}
+		writeJSON(w, 204, nil)
+
+	default:
+		writeJSON(w, 405, M{"error": "method not allowed"})
+	}
+}
+
+func str(m map[string]any, key string) string {
+	if v, ok := m[key].(string); ok { return v }
+	return ""
+}
+func num(m map[string]any, key string) int {
+	if v, ok := m[key].(float64); ok { return int(v) }
+	return 0
 }
 
 // --- Helpers ---