Add plugin telemetry bridge capability

Expose telemetry.track through the plugin SDK and server host bridge, forward plugin-prefixed events into the shared telemetry client, and demonstrate the capability in the kitchen sink example.\n\nCo-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/services/plugin-capability-validator.ts

@@ -68,6 +68,7 @@ const OPERATION_CAPABILITIES: Record<string, readonly PluginCapability[]> = {
   "issue.comments.create": ["issue.comments.create"],
   "activity.log": ["activity.log.write"],
   "metrics.write": ["metrics.write"],
+  "telemetry.track": ["telemetry.track"],
 
   // Plugin state operations
   "plugin.state.get": ["plugin.state.read"],