feat: default to average downsampling

Average consolidation makes every plotted point the true arithmetic mean of
its interval, which is what the Ganglia-style plot appearance depends on.
LTTB deliberately keeps extremes instead, so a plot downsampled with it
cannot be read as interval means.

resolveResampleAlgo used to return an empty string when neither the user nor
the config had chosen an algorithm, and cc-lib's GetResampler maps that to
LTTB. Route every fallback through config.ResampleAlgo() and ship "average"
as the generated and example default.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/graph/resample.go

@@ -63,12 +63,12 @@ func resolveResampleAlgo(ctx context.Context, resampleAlgo *model.ResampleAlgo)
 
 	user := repository.GetUserFromContext(ctx)
 	if user == nil {
-		return ""
+		return config.ResampleAlgo()
 	}
 
 	conf, err := repository.GetUserCfgRepo().GetUIConfig(user)
 	if err != nil {
-		return ""
+		return config.ResampleAlgo()
 	}
 
 	algoVal, ok := conf["plotConfiguration_resampleAlgo"]
@@ -78,12 +78,8 @@ func resolveResampleAlgo(ctx context.Context, resampleAlgo *model.ResampleAlgo)
 		}
 	}
 
-	// Fall back to global default algo
-	if config.Keys.EnableResampling != nil && config.Keys.EnableResampling.DefaultAlgo != "" {
-		return config.Keys.EnableResampling.DefaultAlgo
-	}
-
-	return ""
+	// Fall back to the global default algo
+	return config.ResampleAlgo()
 }
 
 // resolveResolutionFromDefaultPolicy computes a resolution using the global