/code-review and /simplify Skip Redundant Model Invocation

The /code-review and /simplify slash commands now carry disableModelInvocation: true in their skill definition. Previously, Claude's main model re-processed the command after the skill loaded, which was redundant because both skills immediately hand off to an embedded multi-agent workflow. With this flag set, the skill executes its own agentic logic directly without an extra round-trip through the main model. Users should notice no behavioral change, but the commands may start slightly faster and consume fewer tokens on the initial dispatch.