Fix BaseDeps.Logger and BaseDeps.Metrics to return safe defaults when Obsv is nil

Agent-Logs-Url: https://github.com/github/github-mcp-server/sessions/53221b0b-abb4-4138-a147-3ce9e13b379a

Co-authored-by: mattdholloway <918573+mattdholloway@users.noreply.github.com>

Author: Copilot

pkg/github/dependencies.go

@@ -189,15 +189,15 @@ func (d BaseDeps) GetContentWindowSize() int { return d.ContentWindowSize }
 // Logger implements ToolDependencies.
 func (d BaseDeps) Logger(_ context.Context) *slog.Logger {
 	if d.Obsv == nil {
-		return nil
+		return slog.New(slog.DiscardHandler)
 	}
 	return d.Obsv.Logger()
 }
 
 // Metrics implements ToolDependencies.
 func (d BaseDeps) Metrics(ctx context.Context) metrics.Metrics {
 	if d.Obsv == nil {
-		return nil
+		return metrics.NewNoopMetrics()
 	}
 	return d.Obsv.Metrics(ctx)
 }