tz: server-wide display timezone via TZ env var (default EST/EDT)

User-reported issue: server logs were timestamped in UTC ("05:36:20"
when local was ~01:36 EDT), and the PDF report's "Created" footer
similarly showed raw UTC.  Inconsistent with the modal which already
converts to browser local via toLocaleString.

Solution: standard Linux TZ env var.  Set once in the container, and:
  - Python's datetime.now() uses local
  - Logging module's timestamps use local
  - matplotlib renderers + report_pdf formatters use local
  - astimezone() conversions resolve to the configured TZ

DB columns stay UTC (created_at uses SQLite's strftime('%Y-...Z', 'now')
which is always UTC, regardless of TZ env var — proper "store UTC,
display local" pattern).

Changes:
  - Dockerfile: install tzdata (python:3.11-slim omits the timezone
    database), set default TZ=America/New_York
  - sfm/report_pdf.py: _fmt_iso_to_bw and _split_iso_to_date_time now
    convert UTC inputs (Z-suffixed) to local via astimezone(); naïve
    inputs (BW recorded-at, already unit-local) returned as-is.
    New _to_display_local helper centralizes the logic.
  - "Created" line in the PDF page footer now uses the converted
    timestamp.

Override per-deployment via the TZ env var in docker-compose
(separate commit on terra-view side).

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

Dockerfile

@@ -2,10 +2,21 @@ FROM python:3.11-slim
 
 WORKDIR /app
 
+# tzdata is required for the TZ env var to take effect (python:slim
+# omits the timezone database).  Without it, datetime.now() / logging
+# / matplotlib all stay in UTC regardless of TZ.  Default zone gets
+# set further down via ENV; users override per-deployment via the
+# `TZ` env var in docker-compose.
 RUN apt-get update && \
-    apt-get install -y --no-install-recommends curl && \
+    apt-get install -y --no-install-recommends curl tzdata && \
     rm -rf /var/lib/apt/lists/*
 
+# Default display timezone — applied to server logs, datetime.now(),
+# matplotlib rendered timestamps, and any naïve-vs-aware datetime
+# conversions in the PDF renderer.  Override via TZ env var in
+# docker-compose; storage in the DB is always UTC regardless.
+ENV TZ=America/New_York
+
 COPY pyproject.toml requirements.txt ./
 COPY minimateplus ./minimateplus
 COPY micromate    ./micromate

sfm/report_pdf.py

@@ -348,9 +348,11 @@ def render_event_report_pdf(rd: ReportData) -> bytes:
     # Page footer (common to both layouts) — Created date + event id.
     # Pushed to the very page bottom so it doesn't collide with the
     # waveform footer scale / trigger legend lines just above.
+    # Convert UTC server_received_at to local for display.
+    created_local = _fmt_iso_to_bw(rd.server_received_at) if rd.server_received_at else "—"
     fig.text(
         0.07, 0.005,
-        f"Created: {rd.server_received_at or '—'}  •  seismo-relay",
+        f"Created: {created_local}  •  seismo-relay",
         fontsize=6, color="#888", ha="left",
     )
     fig.text(
@@ -419,31 +421,50 @@ def _render_histogram_layout(fig, rd: ReportData) -> None:
     _draw_histogram_subplot(fig, gs[3], rd)
 
 
+def _to_display_local(iso: str):
+    """Parse an ISO timestamp and return a datetime in the system's local
+    timezone (set by the TZ env var, default America/New_York via the
+    Dockerfile).
+
+    Behaviour:
+      - "...Z" or "...+HH:MM" suffix → tz-aware UTC → converted to local
+      - Naïve "YYYY-MM-DDTHH:MM:SS" (no tz) → returned as-is.  This
+        matches the convention used elsewhere in seismo-relay: BW's
+        recorded-at timestamps are naïve and ALREADY in the unit's
+        local clock; we don't second-guess them.
+    """
+    import datetime as _dt
+    dt = _dt.datetime.fromisoformat(iso.replace("Z", "+00:00"))
+    if dt.tzinfo is not None:
+        # Convert from UTC (or other tz) → local per the TZ env var.
+        # astimezone() without arg uses the system timezone.
+        dt = dt.astimezone()
+    return dt
+
+
 def _fmt_iso_to_bw(iso: Optional[str]) -> Optional[str]:
-    """Convert a ISO-8601 timestamp like '2026-05-16T22:30:37' to BW's
-    display format '22:30:37 May 16, 2026'.  Returns input unchanged if
-    it doesn't look like ISO."""
+    """Convert an ISO-8601 timestamp to BW's display format
+    '22:30:37 May 16, 2026'.  UTC inputs (with Z suffix) are
+    converted to the system's local timezone first; naïve inputs
+    are formatted as-is.  Returns input unchanged on parse failure."""
     if not iso or "T" not in iso:
         return iso
     try:
-        import datetime as _dt
-        dt = _dt.datetime.fromisoformat(iso.replace("Z", "+00:00"))
-        return dt.strftime("%H:%M:%S %B %d, %Y").replace(" 0", " ")
+        return _to_display_local(iso).strftime("%H:%M:%S %B %d, %Y").replace(" 0", " ")
     except Exception:
         return iso
 
 
 def _split_iso_to_date_time(iso: Optional[str]) -> tuple[Optional[str], Optional[str]]:
-    """Split an ISO timestamp into BW-formatted ("May 27 /26", "06:06:14")
+    """Split an ISO timestamp into BW-formatted ('May 27 /26', '06:06:14')
     date+time strings.  Used for the histogram stats table where the
-    Date and Time rows are presented separately.  Returns (None, None)
-    if the input isn't a valid ISO datetime."""
+    Date and Time rows are presented separately.  UTC inputs are
+    converted to local time first.  Returns (None, None) on parse failure."""
     if not iso:
         return (None, None)
     try:
-        import datetime as _dt
-        dt = _dt.datetime.fromisoformat(iso.replace("Z", "+00:00"))
-        # BW format: "May 27 /26" (3-letter month + 2-digit year)
+        dt = _to_display_local(iso)
+        # BW format: 'May 27 /26' (3-letter month + 2-digit year)
         date_str = dt.strftime("%b %d /%y").replace(" 0", " ")
         time_str = dt.strftime("%H:%M:%S")
         return (date_str, time_str)