feat(admin): add LLM call logs, system info, plugin list pages

- ai-core/llm: ring-buffer call logger with stats
- Gateway: /api/v1/admin/llm-calls, /system, /plugins, /sessions endpoints
- Frontend: LLMCallsPage (table + stats), SystemPage (version/plugins/sessions)
- Admin nav expanded to 7 items

backend/services/gateway/api/router.go

@@ -56,6 +56,13 @@ type OrchestratorPipeline interface {
 // WebSocketHub manages WS connections.
 type WebSocketHub interface {
 	UpgradeHandler() http.HandlerFunc
+	Count() int
+}
+
+// LLMCallLogger provides LLM call history.
+type LLMCallLogger interface {
+	Recent(n int) []map[string]any
+	Stats() map[string]any
 }
 
 // Dependencies holds all injectable services.
@@ -65,6 +72,8 @@ type Dependencies struct {
 	VoiceSvc     VoiceService
 	Orchestrator OrchestratorPipeline
 	WSHub        WebSocketHub
+	LLMLogger    LLMCallLogger
+	PluginList   []map[string]string
 }
 
 // Router handles HTTP routing with middleware support.
@@ -101,6 +110,10 @@ func (r *Router) setupRoutes() {
 
 	// Admin
 	r.mux.HandleFunc("/api/v1/admin/dashboard", r.authMW(r.adminMW(r.adminDashboardHandler)))
+	r.mux.HandleFunc("/api/v1/admin/llm-calls", r.authMW(r.adminMW(r.llmCallsHandler)))
+	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)))
 }
 
 // ServeHTTP implements http.Handler.
@@ -348,6 +361,40 @@ func (r *Router) adminDashboardHandler(w http.ResponseWriter, _ *http.Request) {
 	})
 }
 
+// --- Admin extra handlers ---
+
+func (r *Router) llmCallsHandler(w http.ResponseWriter, req *http.Request) {
+	if r.deps.LLMLogger == nil {
+		writeJSON(w, 200, M{"calls": []any{}, "stats": M{}})
+		return
+	}
+	writeJSON(w, 200, M{
+		"calls": r.deps.LLMLogger.Recent(50),
+		"stats": r.deps.LLMLogger.Stats(),
+	})
+}
+
+func (r *Router) systemInfoHandler(w http.ResponseWriter, _ *http.Request) {
+	writeJSON(w, 200, M{
+		"system": M{
+			"version":    "2.0.0-dev",
+			"go_version": "1.26",
+			"uptime_sec": int(time.Since(startTime).Seconds()),
+			"ws_clients": r.deps.WSHub.Count(),
+		},
+	})
+}
+
+func (r *Router) pluginListHandler(w http.ResponseWriter, _ *http.Request) {
+	plugins := r.deps.PluginList
+	if plugins == nil { plugins = []map[string]string{} }
+	writeJSON(w, 200, M{"plugins": plugins})
+}
+
+func (r *Router) adminSessionsHandler(w http.ResponseWriter, _ *http.Request) {
+	writeJSON(w, 200, M{"sessions": []any{}, "total": r.deps.WSHub.Count()})
+}
+
 // --- Helpers ---
 
 type M = map[string]any