event-modal: relabel "Captured at" → "Time received"

"Captured at" was easily misread as "when the device captured the
event" — but that's the event's Timestamp at the top of the modal
(unit-local trigger time).  source.captured_at is actually when SFM
received and stored the event.  New label avoids the ambiguity, and
the hover tooltip spells it out for anyone unsure.

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

backend/static/event-modal.js

@@ -647,7 +647,9 @@
         <div class="grid grid-cols-1 sm:grid-cols-2 gap-x-6 gap-y-2 text-sm">
             <div class="sm:col-span-2"><span class="text-gray-500">Blastware file</span> <span class="font-mono text-xs ml-1">${_esc(bw.filename || '—')}</span> ${sizeKb ? `<span class="text-xs text-gray-500 ml-2">(${sizeKb} KB)</span>` : ''}</div>
             <div class="sm:col-span-2"><span class="text-gray-500">SHA-256</span> <span class="font-mono text-xs ml-1 break-all">${_esc(bw.sha256 || '—')}</span></div>
-            <div><span class="text-gray-500">Captured at</span> <span class="font-medium ml-1">${_esc(src.captured_at ? src.captured_at.slice(0, 19).replace('T', ' ') : '—')}</span></div>
+            <div title="When SFM received and stored this event — NOT the unit-local trigger time (see Timestamp at the top of the modal for that).">
+                <span class="text-gray-500">Time received</span> <span class="font-medium ml-1">${_esc(src.captured_at ? src.captured_at.slice(0, 19).replace('T', ' ') : '—')}</span>
+            </div>
             <div><span class="text-gray-500">Tool version</span> <span class="font-mono text-xs ml-1">${_esc(src.tool_version || '—')}</span></div>
         </div>`;
     }