feat: add calibration sync system.

templates/settings.html

@@ -472,6 +472,20 @@
             <button onclick="saveCalibrationDefaults()" class="mt-6 px-6 py-3 bg-seismo-orange hover:bg-orange-600 text-white rounded-lg transition-colors">
                 Save Defaults
             </button>
+
+            <div class="mt-8 pt-6 border-t border-gray-200 dark:border-gray-700">
+                <h3 class="text-lg font-semibold text-gray-900 dark:text-white mb-2">Sync from SFM events</h3>
+                <p class="text-sm text-gray-500 dark:text-gray-400 mb-3">
+                    Reads <code>calibration_date</code> from each seismograph's most recent event sidecar and updates
+                    <em>Last Calibrated</em> when the device reports a newer date than what's stored.
+                    Manual edits made after the latest event are preserved. Runs automatically once a day.
+                </p>
+                <button onclick="runCalibrationSync()" id="cal-sync-btn"
+                        class="px-6 py-3 bg-blue-600 hover:bg-blue-700 text-white rounded-lg transition-colors">
+                    Sync now
+                </button>
+                <div id="cal-sync-result" class="mt-3 text-sm text-gray-700 dark:text-gray-300"></div>
+            </div>
         </div>
     </div>
 </div>
@@ -890,6 +904,41 @@ async function saveCalibrationDefaults() {
     }
 }
 
+async function runCalibrationSync() {
+    const btn = document.getElementById('cal-sync-btn');
+    const out = document.getElementById('cal-sync-result');
+    btn.disabled = true;
+    const originalLabel = btn.textContent;
+    btn.textContent = 'Syncing…';
+    out.textContent = '';
+    out.className = 'mt-3 text-sm text-gray-700 dark:text-gray-300';
+
+    try {
+        const response = await fetch('/api/calibration/sync', { method: 'POST' });
+        const data = await response.json();
+        if (!response.ok) {
+            out.className = 'mt-3 text-sm text-red-600 dark:text-red-400';
+            out.textContent = 'Error: ' + (data.detail || response.statusText);
+            return;
+        }
+        const parts = [
+            `Checked ${data.checked}`,
+            `Updated ${data.updated}`,
+            `Already in sync ${data.already_in_sync}`,
+            `Manual kept ${data.skipped_manual_newer}`,
+            `No event ${data.no_event}`,
+        ];
+        if (data.errors) parts.push(`Errors ${data.errors}`);
+        out.textContent = parts.join(' · ');
+    } catch (error) {
+        out.className = 'mt-3 text-sm text-red-600 dark:text-red-400';
+        out.textContent = 'Error: ' + error.message;
+    } finally {
+        btn.disabled = false;
+        btn.textContent = originalLabel;
+    }
+}
+
 // ========== DATA TAB - IMPORT/EXPORT ==========
 
 // Merge Mode Import