* feat(scheduler): add interval schedule type
Allow scheduled tasks to fire every N seconds from last dispatch, not
only wall-clock cron or a single run_at. Cadence is UTC now+N with no
missed-beat catch-up, bounded by min_once_delay_seconds and 30 days.
* fix(scheduler): let interval tasks create, edit, and keep next run
Create/edit now keep every_seconds. Unchanged interval spec no longer
resets next_run_at, including timezone-only PATCH.
* fix(scheduler): keep non-minute intervals on edit
Stop rounding every_seconds to whole minutes in the form. Values that
are not whole minutes or hours now use a seconds unit so edit/duplicate
round-trips the stored cadence instead of rewriting it and resetting
next_run_at. Document that min_once_delay_seconds is also the interval
floor.
* fix(scheduler): clamp interval seconds to the default 60s floor
The new seconds unit allowed 1–59, which the API rejects under the
default min_once_delay_seconds. Clamp the form to >= 60 and show the
floor next to the preview. Also mention interval in the scheduler
field_doc, matching config.example.yaml.
* fix(scheduler): do not clamp interval amount while typing
Keystroke clamp made 90 become 9 -> 60, then 600, and backspace could
not leave 60. Keep the raw field text and apply the 60s floor on blur
and emit only.
* test(scheduler): cover interval input editing
* fix(frontend): preserve saved interval cadence until edited
* style(tests): format scheduled task router tests
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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