V118 OBSERVATION TIME = FIRST ARRIVAL REAPPLY

Base
- Built from V117, preserving the quick finite-fault Excel-style editor fixes.

What changed
- Reapplies the V98 observation-time behavior safely.
- For observation_arrival height/peak update bulletins, observed_time_s is no longer updated to the peak-update/report time.
- observed_time_s and observation_time_s now stay fixed to the first positive-arrival time for that observation point.
- report_bucket_s and scheduled_bulletin_s still show the current 5-minute report/update bucket.

Why
- peak_updated / individual_peak_updated tells Scratch whether the observation point made a new individual maximum.
- observed_time_s should represent first-wave arrival time, not the time of later maximum update.
