Move tool_registry_incident_triage tests to test/<sample-dir>/, add to README

Followup to a7935da to bring the new sample into compliance with samples-ruby
CONTRIBUTING.md conventions:

- Tests now at test/tool_registry_incident_triage/ (root-level test/ subdir
  per CONTRIBUTING.md "If needed, add tests in test/<sample-dir>/<subject>_test.rb").
- Added entry to root README example list (alphabetical).

Per-example Gemfile retained (rails_app precedent for samples needing local
SDK pin or non-trivial deps).

Author: lex00

README.md

@@ -35,6 +35,7 @@ Prerequisites:
 * [rails_app](rails_app) - Basic Rails API application using Temporal workflows and activities.
 * [saga](saga) - Using undo/compensation using a very simplistic Saga pattern.
 * [sorbet_generic](sorbet_generic) - Proof of concept of how to do _advanced_ Sorbet typing with the SDK.
+* [tool_registry_incident_triage](tool_registry_incident_triage) - LLM-driven incident triage activity using `Temporalio::Contrib::ToolRegistry`. Demonstrates `AgenticSession`, MCP HTTP integration, human-in-the-loop, and a testable activity refactor.
 * [updatable_timer](updatable_timer) - Demonstrates a blocking sleep that can be updated.
 * [worker_specific_task_queues](worker_specific_task_queues) - Use a unique Task Queue for each Worker to run a sequence of Activities on the same Worker.
 * [worker_versioning](worker_versioning) - Use the Worker Versioning feature to more easily version your workflows & other code.