Loads cron/jobs.json and asserts: unique names, valid cron expressions
(APScheduler parseable), bool enabled field; kind:"shell" entries must
have non-empty channel, non-empty command list of strings, valid
report_on, and timeout within [1, 3600] when present; claude entries
must have non-empty prompt, valid model, list-typed allowed_tools.
Sanity-checks that shell commands reference existing scripts in the
repo and that no imported claude prompt still points at /home/moltbot/clawd/.