fix(node): Drop deprecated forceTransaction in Mastra exporter

Oxlint no-deprecated fails on the new startInactiveSpan call; nesting still uses parentSpan ?? activeSpan, and a missing parent already creates a root span.

Co-Authored-By: Cursor Grok 4.6 <cursoragent@cursor.com>

Author: RulaKhaled

packages/server-utils/src/ai/mastra/index.ts

@@ -128,9 +128,8 @@ export class SentryMastraExporter implements MastraObservabilityExporter {
     const sentrySpan = startInactiveSpan({
       name: getSpanName(span),
       startTime: span.startTime,
-      // Nest under the Mastra parent, else the active request span; only force a transaction if neither exists.
+      // Prefer the Mastra parent so the tree stays together; else the active request span.
       parentSpan: parentSpan ?? activeSpan,
-      forceTransaction: !parentSpan && !activeSpan,
       attributes: {
         ...this._attributesFor(span),
         [SEMANTIC_ATTRIBUTE_SENTRY_OP]: getOperation(span.type)?.op,