fix: resolve dashboard 401 and 500 errors

Restricted AuthMiddleware to /v1 group to prevent dashboard session interference. Robustified analytics SQL queries with COALESCE to handle empty datasets.

internal/server/dashboard.go

@@ -304,7 +304,7 @@ func (s *Server) handleTimeSeries(c *gin.Context) {
 
 	query := fmt.Sprintf(`
 		SELECT 
-			strftime('%%Y-%%m-%%d', timestamp) as bucket,
+			COALESCE(strftime('%%Y-%%m-%%d', timestamp), 'unknown') as bucket,
 			COUNT(*) as requests,
 			COALESCE(SUM(total_tokens), 0) as tokens,
 			COALESCE(SUM(cost), 0.0) as cost
@@ -444,7 +444,7 @@ func (s *Server) handleDetailedUsage(c *gin.Context) {
 
 	query := fmt.Sprintf(`
 		SELECT 
-			strftime('%%Y-%%m-%%d', timestamp) as date,
+			COALESCE(strftime('%%Y-%%m-%%d', timestamp), 'unknown') as date,
 			COALESCE(client_id, 'unknown') as client,
 			COALESCE(provider, 'unknown') as provider,
 			COALESCE(model, 'unknown') as model,