viewers: smoother mic dBL chart + restore binary/TXT download links

Two issues spotted in the modal:

1. Mic dBL chart looked spikey/discontinuous — isolated bars at 80-95
   with gaps in between.  Cause: _psiToDbl() returns null for zero or
   negative samples, and most mic samples on a quiet event sit at the
   digitization noise floor where they're effectively zero.  Result:
   the chart only renders the moments when instantaneous SPL exceeded
   the Y-axis bottom — looks like a sound trigger gate.

   Fix: new _psiToDblForChart() rectifies the AC waveform (abs), then
   converts to dBL, then floors at MIC_DBL_FLOOR=60 dBL.  Chart now
   has a continuous 60 dBL baseline with peaks above it — matches how
   acoustic engineers expect SPL-vs-time.  Y-axis bottom pinned to
   MIC_DBL_FLOOR, top to peak + 5 dB headroom.  Peak label still uses
   the unrectified _psiToDbl so the displayed peak value is exact.

2. Filename in Source/Files block was unlinked.  Endpoint exists
   (/db/events/{id}/blastware_file) — just wasn't wired to the modal.
   Made it a clickable download link.  Same treatment for the
   preserved .TXT — added "(download .TXT)" link next to source kind
   when source.txt_filename is populated (events ingested after the
   .TXT preservation feature landed; older events show no link).

Applied to both the inline modal in sfm_webapp.html and the
standalone /events page in event_browser.html.

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

sfm/sfm_webapp.html

@@ -2589,6 +2589,23 @@ function _psiToDbl(psi) {
   return 20 * Math.log10(psi / DBL_REF);
 }
 
+// Per-sample mic display floor.  Sound pressure AC samples spend most
+// of their time at the digitization noise floor (1-2 ADC counts ≈ ~20-40
+// dBL).  Rendering each one as null/-inf produces a spikey discontinuous
+// chart of "moments when sound briefly exceeded 80 dBL" — confusing.
+// Instead we rectify (abs the AC waveform), convert to dBL, and floor
+// anything below MIC_DBL_FLOOR so the chart has a continuous baseline
+// with peaks rising above it.  Matches how acoustic engineers expect to
+// see SPL-vs-time.
+const MIC_DBL_FLOOR = 60;
+function _psiToDblForChart(psi) {
+  if (psi == null) return MIC_DBL_FLOOR;
+  const a = Math.abs(psi);
+  if (a === 0) return MIC_DBL_FLOOR;
+  const dbl = 20 * Math.log10(a / DBL_REF);
+  return dbl > MIC_DBL_FLOOR ? dbl : MIC_DBL_FLOOR;
+}
+
 // Adaptive decimal formatter — scientific notation is reserved for truly
 // extreme values (10000+ or sub-0.0001).  Normal-range values (most peaks
 // fall here) render as decimals with sensible precision.  Replaces the
@@ -2649,10 +2666,14 @@ function _renderScWaveform(data) {
     let chPeak = chData.peak;
 
     // Mic channel: convert from raw psi to dB(L) when user prefers dBL
-    // (default).  Mic samples that are zero/negative become null (Chart.js
-    // renders them as gaps in line mode, zero-height bars in histogram mode).
+    // (default).  Per-sample values use _psiToDblForChart which rectifies
+    // (abs) the AC waveform and floors at MIC_DBL_FLOOR so the chart is
+    // continuous with a baseline + peaks above it, instead of a sparse
+    // pattern of isolated spikes for "moments when sound briefly exceeded
+    // the Y-axis bottom".  The peak label uses _psiToDbl with the
+    // unrectified peak (preserves the true measurement).
     if (ch === 'MicL' && chUnit === 'psi' && micUnit === 'dBL') {
-      values = values.map(_psiToDbl);
+      values = values.map(_psiToDblForChart);
       chPeak = _psiToDbl(chPeak);
       chUnit = 'dB(L)';
     }
@@ -2736,6 +2757,13 @@ function _renderScWaveform(data) {
       }
       const padded = (absMax || 1) * 1.10;
       yBounds = { min: -padded, max: padded };
+    } else if (ch === 'MicL' && micUnit === 'dBL') {
+      // Pin baseline at the chart floor (which matches what we flooded
+      // null/quiet samples to), top at the actual peak + a few dB headroom.
+      const peakDbl = (typeof chPeak === 'number' && isFinite(chPeak))
+        ? chPeak + 5
+        : 100;
+      yBounds = { min: MIC_DBL_FLOOR, max: Math.max(peakDbl, MIC_DBL_FLOOR + 20) };
     }
 
     _scCharts[ch] = new Chart(canvas, {
@@ -2882,10 +2910,42 @@ function _renderSidecar(data) {
   document.getElementById('sc-f-operator').textContent = pi.operator        || '—';
   document.getElementById('sc-f-loc').textContent      = pi.sensor_location || '—';
 
-  document.getElementById('sc-f-bw').textContent       = bw.filename        || '—';
+  // Filename rendered as a clickable download link for the original BW
+  // binary.  Same endpoint the live-device viewer uses for stored events
+  // (/db/events/{id}/blastware_file).
+  const bwCell = document.getElementById('sc-f-bw');
+  bwCell.innerHTML = '';
+  if (bw.filename && _scCurrentEventId) {
+    const a = document.createElement('a');
+    a.href = `${api()}/db/events/${_scCurrentEventId}/blastware_file`;
+    a.textContent = bw.filename;
+    a.download = bw.filename;
+    a.title = 'Download original BW event binary';
+    a.style.color = 'var(--accent, #58a6ff)';
+    a.style.textDecoration = 'underline';
+    bwCell.appendChild(a);
+  } else {
+    bwCell.textContent = '—';
+  }
   document.getElementById('sc-f-bwsize').textContent   = bw.filesize != null ? `${bw.filesize} bytes` : '—';
   document.getElementById('sc-f-sha').textContent      = bw.sha256          || '—';
-  document.getElementById('sc-f-src').textContent      = src.kind           || '—';
+  // Source kind + a download link for the preserved BW ASCII report
+  // (.TXT), when available.  Only events ingested after 2026-05-27
+  // have the .TXT preserved; older events show "—".
+  const srcCell = document.getElementById('sc-f-src');
+  srcCell.innerHTML = '';
+  srcCell.appendChild(document.createTextNode(src.kind || '—'));
+  if (src.txt_filename && _scCurrentEventId) {
+    const a = document.createElement('a');
+    a.href = `${api()}/db/events/${_scCurrentEventId}/ascii_report.txt`;
+    a.textContent = ' (download .TXT)';
+    a.download = src.txt_filename;
+    a.title = 'Download preserved BW ASCII report';
+    a.style.color = 'var(--accent, #58a6ff)';
+    a.style.marginLeft = '8px';
+    a.style.fontSize = '11px';
+    srcCell.appendChild(a);
+  }
   // captured_at has a "Z" suffix (UTC); _fmtTs converts to browser local
   // — matches the BW-reported recorded-at, no more "21:59:57 vs it's 6 PM"
   // confusion from operators reading the raw UTC value.