fix: restore working repository links for SnapTrace and NullFlix

- Both repositories are accessible and working
- Reverting previous placeholder text changes

Author: codyde

docs/platforms/javascript/common/tracing/span-metrics/examples.mdx

@@ -169,7 +169,7 @@ What to monitor with span metrics:
 
 ## Media Upload with Background Processing (React + Express)
 
-Example Repository: _Coming soon - sample repository in development_
+Example Repository: [SnapTrace](https://github.com/getsentry/snaptrace)
 
 **Challenge:** Track user-perceived upload time, server-side validation, and async media processing (optimization, thumbnail generation) while maintaining trace continuity across async boundaries.
 
@@ -376,7 +376,7 @@ What to monitor with span metrics:
 
 ## Search Autocomplete (debounced, cancellable, performance monitoring)
 
-Example Repository: _Coming soon - sample repository in development_
+Example Repository: [NullFlix](https://github.com/getsentry/nullflix-tracing-sample)
 
 **Challenge:** Users type quickly in search; you need to debounce requests, cancel in-flight calls, handle errors gracefully, and monitor performance across different query types while keeping latency predictable.