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>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "seismo-relay"
-version = "0.19.0"
+version = "0.20.0"
 description = "Python client and REST server for MiniMate Plus seismographs"
 requires-python = ">=3.10"
 dependencies = [