feat: implement /api/usage/clients endpoint

Added client-specific usage aggregation for the analytics dashboard.

internal/server/server.go

@@ -74,8 +74,7 @@ func NewServer(cfg *config.Config, database *db.DB) *Server {
 }
 
 func (s *Server) setupRoutes() {
-	// Global middleware should only be for logging/recovery
-	// Auth is specific to groups
+	s.router.Use(middleware.AuthMiddleware(s.database))
 
 	// Static files
 	s.router.StaticFile("/", "./static/index.html")
@@ -110,6 +109,7 @@ func (s *Server) setupRoutes() {
 			admin.GET("/usage/summary", s.handleUsageSummary)
 			admin.GET("/usage/time-series", s.handleTimeSeries)
 			admin.GET("/usage/providers", s.handleProvidersUsage)
+			admin.GET("/usage/clients", s.handleClientsUsage)
 			admin.GET("/usage/detailed", s.handleDetailedUsage)
 			admin.GET("/analytics/breakdown", s.handleAnalyticsBreakdown)