release: v0.13.1 — mic chart defaults to psi (matches PDF)

v0.13.0 shipped the mic_unit_pref default as "dBL", which made the
website chart's mic axis inconsistent with the PDF report (which
renders psi).  Original brief was always "psi on charts, dBL on
peaks" — I implemented the default backwards.  Operator caught it
within an hour of rollout.

Same-day patch:
- backend/models.py: default "dBL" → "psi"
- migrate_add_mic_unit_pref.py: idempotent across both fresh DB
  ("add column with psi default") and v0.13.0 upgrade ("flip dBL
  rows to psi").  One-row table, freshness assumed.
- backend/routers/settings.py: GET/PUT fallback "dBL" → "psi"
- templates/settings.html: dropdown's `selected` flag moves to psi
  + reorders options + relabels with "(matches PDF report)" hint
- backend/static/event-modal.js: module-level fallback + branch
  conditions flip to make psi the unset/error default

Includes the "Captured at" → "Time received" relabel from earlier
in the day (already-shipped commit 43c804d) rolled into the
release notes.

Migration is idempotent + safe to re-run; rolled out on the dev
container during this commit's smoke test.

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

templates/settings.html

@@ -130,8 +130,8 @@
                     </label>
                     <select id="mic-unit-pref"
                             class="w-full max-w-md px-4 py-2 text-gray-900 dark:text-gray-100 bg-gray-50 dark:bg-gray-700 border border-gray-300 dark:border-gray-600 rounded-lg focus:outline-none focus:ring-2 focus:ring-seismo-orange">
-                        <option value="dBL" selected>dB(L) — sound pressure level</option>
-                        <option value="psi">psi — raw pressure</option>
+                        <option value="psi" selected>psi — raw pressure (matches PDF report)</option>
+                        <option value="dBL">dB(L) — sound pressure level</option>
                     </select>
                     <p class="text-xs text-gray-500 dark:text-gray-400 mt-1">
                         Applies only to the waveform chart inside the event detail modal.  Peak values everywhere else (tables, KPIs, modal summary) stay in dB(L) regardless.
@@ -787,7 +787,7 @@ async function loadPreferences() {
         document.getElementById('refresh-interval').value = prefs.auto_refresh_interval || 10;
 
         // Load event-report mic units
-        document.getElementById('mic-unit-pref').value = prefs.mic_unit_pref || 'dBL';
+        document.getElementById('mic-unit-pref').value = prefs.mic_unit_pref || 'psi';
 
         // Load status thresholds
         document.getElementById('ok-threshold').value = prefs.status_ok_threshold_hours || 12;