Cron is a built-in Hermes feature (CLI `hermes cron`, `cronjob` agent
tool, gateway ticker, scheduler in cron/scheduler.py) but croniter has
been gated behind the [cron] optional extra. Users who do a plain
`pip install hermes-agent` can create jobs via /cron but any recurring
cron schedule silently returns next_run_at=None (HAS_CRONITER=False),
which then gets wrapped into a 'state=error' message only after a tick.
Move croniter into core dependencies so scheduled jobs work out of the
box on any install path. The [cron] extra is kept as an empty
passthrough so existing `pip install hermes-agent[cron]` installs and
the [all]/[termux] extras continue to resolve.
Also update the now-stale user-facing error message in
`compute_next_run()` that still tells users to install `hermes-agent[cron]`.
Salvaged from #17234 (authored by @txbxxx) with a corrected premise:
the original PR claimed [cron] wasn't in [all], but it is (pyproject.toml
line 112). The real UX problem is the plain no-extras install path,
which this fix addresses.
9ee540a5e2