Extend the pure scheduler with elapsed_seconds (clock injected), decide_tick
(offset + due + lifecycle action) and resolve_finalize (cancel-race guard),
so the durable loop stops hand-coding elapsed/finished/status checks and only
does I/O. Deletes the runner's private _elapsed_seconds and converges
current_window_offset onto the one pure elapsed computation. The clock-skew
tolerance and cancel-race guard are now unit-testable at the seam.
Add the pure scheduling seam (campaign_scheduler.decide_schedule) that, given a
static plan and window-clock offset, decides which plan entries are due and
whether the window ended — mirroring judgement.combine_case_outcome, with
time_scale confined to the clock mapping so it never touches judgement/report.
The campaign_runner shell maps injected elapsed time to a window offset, spawns
due child Runs through the existing EvalEngine.run(existing_run=...) path with
campaign_id + RunTrigger.CAMPAIGN, and persists spawned-entry indices per entry
for idempotent, restart-recoverable progress. No auto loop yet (ticket 03).
