sfm: Event Report PDF generation (v0.20.0 stub layout)

New endpoint GET /db/events/{id}/report.pdf returns a single-page
letter-portrait PDF for any event with waveform data on disk.

Architecture:
  sfm/report_pdf.py — gather_report_data() assembles fields from
    SeismoDb row + .sfm.json sidecar (bw_report block) + .h5 samples;
    render_event_report_pdf() turns that into PDF bytes via matplotlib.
  sfm/server.py — new endpoint wires them together, streams PDF back
    with Content-Disposition: inline so the browser displays it.
  sfm_webapp.html — new "Download PDF" button in the event modal
    footer that opens the endpoint in a new tab.

Fields surfaced — same coverage as a Blastware Event Report:
  Header metadata (date/time, trigger source, range, sample rate,
                   project, client, operator, location, serial+firmware,
                   battery, calibration, file name)
  Microphone block (PSPL in dB(L) + psi, ZC freq, channel test)
  Per-channel stats (PPV, ZC Freq, Time of Peak, Peak Accel,
                     Peak Disp, Sensor Check) for Tran/Vert/Long
  Peak Vector Sum
  Waveform plot (MicL/Long/Vert/Tran stacked, shared time axis,
                 trigger marker, symmetric Y for geo, zero-anchored
                 mic) — OR per-interval bar chart for histograms.

Rendering pipeline = matplotlib only (vector PDF, no headless-browser
dep).  Adds matplotlib>=3.8 to deps.

Visual layout is approximate until reference PDFs from Instantel land
at docs/reference/instantel/ for iteration.  USBM RI8507 / OSMRE
compliance chart is stubbed (placeholder rectangle) — separate work
item.

Smoke-tested on a K558 waveform event: 77 KB valid PDF, all fields
populated correctly from the snapshot DB.

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

sfm/server.py

@@ -46,7 +46,7 @@ from typing import Optional
 
 # FastAPI / Pydantic
 try:
-    from fastapi import Body, FastAPI, File, HTTPException, Query, UploadFile
+    from fastapi import Body, FastAPI, File, HTTPException, Query, Response, UploadFile
     from fastapi.middleware.cors import CORSMiddleware
     from fastapi.responses import FileResponse, JSONResponse, StreamingResponse
     from pydantic import BaseModel
@@ -2178,6 +2178,32 @@ def db_event_blastware_file(event_id: str) -> FileResponse:
     )
 
 
+@app.get("/db/events/{event_id}/report.pdf")
+def db_event_report_pdf(event_id: str):
+    """Render an Instantel-style Event Report as a PDF.
+
+    Single-page letter portrait, matches the BW Event Report's data
+    coverage and layout (header / mic block / per-channel stats /
+    waveform plot).  V0.20.0 stub — exact visual being iterated
+    against reference PDFs in ``docs/reference/instantel/``.
+
+    Returns 404 if the event is unknown or has no waveform data on
+    disk (same condition as /waveform.json).
+    """
+    from sfm import report_pdf
+    rd = report_pdf.gather_report_data(_get_db(), _get_store(), event_id)
+    if rd is None:
+        raise HTTPException(status_code=404, detail=f"Event {event_id} not found or has no waveform")
+    pdf_bytes = report_pdf.render_event_report_pdf(rd)
+    # Suggested download filename based on the BW file basename.
+    fname = (rd.file_name or event_id).replace(".", "_")
+    return Response(
+        content=pdf_bytes,
+        media_type="application/pdf",
+        headers={"Content-Disposition": f'inline; filename="{fname}_report.pdf"'},
+    )
+
+
 @app.get("/db/events/{event_id}/waveform.json")
 def db_event_waveform_json(event_id: str) -> dict:
     """