Add a heartbeat to a recurring job

A heartbeat monitors a job that already has its own clock. The job pings after successful work. Silence beyond the period and grace window becomes a missed check-in, while the /fail variant reports explicit failure.

Prerequisites

Before using the required tools, check whether they are available. If any are missing, stop and offer the user exactly two choices:

1. Connect Crontap MCP at https://mcp.crontap.com/mcp. MCP access works on every Crontap tier.
2. Configure $CRONTAP_CLIENT_ID and $CRONTAP_API_KEY for the raw API. Raw API access requires Ultra.

Do not silently choose a path or continue until the user selects one.