cron/scheduler.py:run_job() constructed AIAgent(...) without ever calling
discover_mcp_tools(). The CLI and gateway paths do this at startup; cron
jobs inherited none of it and the user's configured mcp_servers were
invisible inside every cron run.
Insert discover_mcp_tools() right before AIAgent(), wrapped in try/except
so a broken MCP server can't kill an otherwise-working cron job. The call
is idempotent: register_mcp_servers() short-circuits on already-connected
servers, so subsequent ticks in the same scheduler process pay ~0ms.
Scoped to the LLM path only; no_agent script jobs skip it entirely.
Closes#4219.
