chore(release): v0.28.0 — offset (DC-baseline) false-trigger detector

Bumps TOOL_VERSION 0.27.0 -> 0.28.0 (drives the SFM /health + OpenAPI version
too). Rolls CHANGELOG [Unreleased] -> v0.28.0.

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

CHANGELOG.md

@@ -8,6 +8,30 @@ All notable changes to seismo-relay are documented here.
 
 ---
 
+## v0.28.0 — 2026-09-02
+
+**Offset (DC-baseline) false-trigger detector.** Productionizes the validated
+pre-trigger detector: a geophone event whose baseline sits off zero and stays
+flat across the record (sensor bumped / settled / drifted) is now flagged and
+surfaced in Terra-View as an `offset` false-trigger reason — catching offsets the
+crest/near-peak spike rule misses (an offset is low-crest and flat).
+
+### Added
+- `shape_metrics.offset_from_samples` / `offset_from_h5`: per geophone channel,
+  `|median(pre-trigger)| ≥ 0.025 in/s` AND `pre/mid/end spread ≤ 0.02` → offset;
+  the consistency test rejects transients (a real event moves one third). Reads
+  the `.h5` samples + the `pretrig_samples` attr, range-aware via the in/s float
+  samples. Constants `OFFSET_FLOOR` / `OFFSET_MAX_SPREAD` are tunable.
+- `events.shape_offset` / `shape_offset_axis` / `shape_offset_pre` /
+  `shape_offset_spread` columns (auto-migrated: `_SCHEMA` + the `_migrate`
+  ADD COLUMN loop), computed at all three ingest paths and by
+  `backfill_event_shape.py`, exposed via `/db/events`.
+
+Requires the shape/offset backfill on the prod store to populate existing events:
+`python scripts/backfill_event_shape.py --db-path … --store-root …`.
+
+---
+
 ## v0.27.0 — 2026-08-28
 
 **Per-sample decoder verification at scale, plus the offset investigation.**

minimateplus/event_file_io.py

@@ -50,7 +50,7 @@ SIDECAR_KIND   = "sfm.event"
 # bumped without a `pip install` re-run — leading to confusing stale
 # version stamps in sidecars.  Bump this constant and CHANGELOG.md
 # together at release time.
-TOOL_VERSION = "0.27.0"
+TOOL_VERSION = "0.28.0"
 
 try:
     # Best-effort: prefer the installed metadata when it's NEWER than the