docs(changelog): waveform event-time fix (exact trigger from binary)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YDXjZCr4RqT2U3QvMDhgzf

CHANGELOG.md

@@ -6,6 +6,22 @@ All notable changes to seismo-relay are documented here.
 
 ## Unreleased
 
+### Fixed
+
+- **Waveform event times were the monitoring-session start, not the trigger
+  (~hours off).**  `read_blastware_file` stamped events with footer `ts1`, which
+  for a waveform is the session start a unit shares across every event that day
+  (a unit arming at 06:00 stamped 06:00 on all of them — the modal and PDF both
+  showed it, since it's the stored value).  The event time is footer `ts2` (the
+  recording stop), and Blastware's trigger = `ts2 - record time`.  The record
+  time is a big-endian float32 in the recording-setup config block (30 bytes
+  before the `Standard Recording Setup` marker), so the **exact trigger is now
+  recovered from the binary alone** — all 7 BE12844 oracle events decode to
+  their exact Blastware time (e.g. N844LQHB 10:33:29), no paired `.TXT` needed.
+  Histograms keep `ts1` (the ~24 h window start).  A paired report's
+  `event_datetime` stays authoritative (unit-clock drift).
+  ⚠ **Needs a re-decode backfill** to correct existing stored events' timestamps.
+
 ### Added
 
 - **Diagnostics tab in the SFM standalone webapp.**  Surfaces the device