Fix frontend OTel spans hierarchy

[reakaleek]

Problem

HTTP fetch spans from automatic instrumentation weren't appearing as children of custom spans (e.g., "execute search"). They were appearing as siblings instead.

Solution

Refactored traceSpan() helper to use startActiveSpan() instead of startSpan(). This automatically sets the span as the active context, allowing automatic instrumentation to properly create child spans.

Result

• Fetch calls now appear as children of their parent spans
• Proper trace hierarchy in telemetry
• Cleaner, more idiomatic OpenTelemetry code