release: v0.20.0 — PDF + parser polish

Closes out the Event-Report PDF iteration started in v0.17.x and ships
the parser fixes the real-world events were tripping over.

Today's additions on top of the pre-v0.20 unreleased body:

- Server-wide display TZ via the TZ env var (default America/New_York
  on prod).  Affects server logs, the PDF report's "Created" footer,
  matplotlib datetime axes.  DB columns stay UTC.  Dockerfile now
  installs tzdata.
- ZC Freq "above-range" handling — parser stores 100.0 +
  zc_freq_above_range flag for BW's ">100 Hz" marker.  Renders as
  >100 in the PDF stats table, both modals (inline on webapp Peaks,
  new column on event-browser table).
- scripts/backfill_sidecars.py --reparse-txt — re-runs the current
  parser against the preserved _ASCII.TXT and overwrites the
  sidecar's bw_report block.  Lets parser fixes reach old events
  without re-forwarding.  Validated end-to-end against ~10k prod
  events.

Fixes shipped today:
- histogram_interval_size_s missing from ReportData → every
  histogram PDF render 500'd.
- Histogram PDF geo channels now share a nice-quantized y-axis
  (0.005-LSB-aware 1-2-5 step sequence) instead of auto-scaling
  per channel + inventing sub-LSB "0.003 in/s/div" footer labels.

Roadmap delta: closes the BW ASCII parser "PPV-miss on some TXT
formats", "histogram-specific structural fields", and ">100 Hz value
parsing" items.  Adds a new entry for the byte[5]==0 histogram body
sub-format observed on S353 events.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -1,4 +1,4 @@
-# seismo-relay  `v0.19.0`
+# seismo-relay  `v0.20.0`
 
 A ground-up replacement for **Blastware** — Instantel's aging Windows-only
 software for managing seismographs.  Supports both the **MiniMate Plus
@@ -35,6 +35,16 @@ over direct RS-232 or cellular modem (Sierra Wireless RV50 / RV55).
 > and storage layer dispatch deterministically instead of sniffing
 > filenames.  Self-applying migration backfills existing rows from the
 > binary filename extension.
+> **v0.20.0 (2026-05-28)** closes out the Event-Report PDF iteration
+> started in v0.17.x: histogram layouts render correctly against BW
+> reference PDFs, the ASCII parser handles real-world edge cases
+> (`OORANGE`, `>100 Hz`, histogram timestamps), and per-channel ZC
+> Freq is surfaced in both modals (event browser + main webapp).
+> Adds a server-wide `TZ` env var so operator-visible timestamps
+> render in local time instead of UTC.  New
+> `scripts/backfill_sidecars.py --reparse-txt` lets parser fixes be
+> applied retroactively to existing events without re-forwarding,
+> using the `.TXT` files preserved at ingest time.
 > See [CHANGELOG.md](CHANGELOG.md) for full version history.
 
 ---
@@ -536,10 +546,10 @@ Implementation steps (concrete):
 
 ### BW ASCII report parser enhancements (built in v0.16.0)
 
-- [ ] **PPV field misses on certain TXT formats.**  Discovered 2026-05-22 during the histogram-codec backfill validation: a handful of events (5 in prod) have a `bw_report` block where `peaks.{tran,vert,long}.ppv_ips` and `peaks.vector_sum.ips` are all `None`, despite the parser correctly extracting every OTHER field for the same channels (zc_freq_hz, time_of_peak_s, peak_accel_g, peak_disp_in).  Symptom on the DB side: `peak_vector_sum=0` after a `--force` backfill that overlays from the parsed bw_report dict.  Affected events on prod include `T190LD5Q.LK0W`, `T438L713.RY0W`, `K557L3YM.OE0W`.  Root cause likely a regex or format mismatch for the "PPV" header line in those specific firmware/event-type outputs.  Once fixed, re-forwarding the events from series3-watcher will re-populate the `bw_report` blocks correctly.
-- [ ] **Histogram-specific structural fields.**  Current parser handles the shared fields (PPV, ZC Freq, sensor self-check, project) but silently drops histogram-only fields: `Histogram Start/Stop Time`, `Histogram Start/Stop Date`, `Number of Intervals`, `Interval Size`, per-channel `Peak Time` + `Peak Date` (absolute timestamps rather than the waveform's `Time of Peak` relative seconds).
+- [x] **PPV field misses on certain TXT formats.** ✅ v0.20.0 — root cause was the `OORANGE` (Out Of Range) saturation marker that BW writes when a channel exceeds its full-scale; `_parse_number()` returned None for the non-numeric value.  Parser now substitutes `geo_range_ips` as a lower bound + sets `ppv_saturated` flag.  All 5 prod events (T190LD5Q.LK0W, T438L713.RY0W, K557L3YM.OE0W, + 2 others) now parse cleanly.
+- [x] **Histogram-specific structural fields.** ✅ v0.20.0 — `Histogram Start/Stop Time+Date`, `Number of Intervals`, `Interval Size`, per-channel `Peak Time` + `Peak Date`, and `Peak Vector Sum Date` all parse now.  Land in the sidecar's `bw_report.histogram` block.
 - [ ] **Histogram interval bin-table parsing.**  Trailing 792-row table (per-interval Peak/Freq per channel + MicL) in histogram TXTs is unparsed.  Probably too big for the sidecar JSON; may want a separate `.histogram.h5` companion file.
-- [ ] **`>100 Hz` value parsing.**  Histogram TXTs use `>100 Hz` for out-of-range ZC freq; current `_parse_number()` returns `None` for these (loses information).
+- [x] **`>100 Hz` value parsing.** ✅ v0.20.0 — parser now mirrors the OORANGE pattern: stores 100.0 on `zc_freq_hz` + sets `zc_freq_above_range` flag.  PDF + both modals render `>100 Hz` instead of `—`.
 
 ### Ingestion gaps