fix(javascript): advertise the exact empty seed rule and match empty API keys

Express the empty-seed rule as a JSON-Schema-representable union, so
the advertised trace_application_feature schema rejects what the
server rejects, and match context-bridge seeds on the exact api_key.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/domain/javascriptFeatureSeed.ts

@@ -132,7 +132,7 @@ const memberFieldSuffixes = new Set([
 
 const relevantFields = {
   route: [".label", ".value", ".path"],
-  api: [".label", ".api_name", ".key", ".methods", ".members"],
+  api: [".label", ".api_name", ".api_key", ".key", ".methods", ".members"],
   channel: [".label", ".channel", ".key"],
   module: [
     ".label",