feat: complete dashboard API migration

Implemented missing system, analytics, and auth endpoints. Verified parity with frontend expectations.

internal/server/server.go

@@ -97,6 +97,7 @@ func (s *Server) setupRoutes() {
 		api.POST("/auth/login", s.handleLogin)
 		api.GET("/auth/status", s.handleAuthStatus)
 		api.POST("/auth/logout", s.handleLogout)
+		api.POST("/auth/change-password", s.handleChangePassword)
 		
 		// Protected dashboard routes (need admin session)
 		admin := api.Group("/")
@@ -104,6 +105,7 @@ 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("/analytics/breakdown", s.handleAnalyticsBreakdown)
 			
 			admin.GET("/clients", s.handleGetClients)
@@ -124,6 +126,9 @@ func (s *Server) setupRoutes() {
 			admin.DELETE("/users/:id", s.handleDeleteUser)
 
 			admin.GET("/system/health", s.handleSystemHealth)
+			admin.GET("/system/settings", s.handleGetSettings)
+			admin.POST("/system/backup", s.handleCreateBackup)
+			admin.GET("/system/logs", s.handleGetLogs)
 		}
 	}