fix(viewer): BUG1d switchTab before renderUSV to fix Plotly on hidden divs

Plotly.react fails silently on display:none divs.
Switch tab to USV first, then render so divs are visible when Plotly mounts.

viewer/index.html

@@ -1228,9 +1228,9 @@ async function loadSortieData(sortieId) {
     const usvResp = await fetch(`${API2}/sorties/${encodeURIComponent(sortieId)}/usv`);
     if (usvResp.ok) {
       const usvData = await usvResp.json();
-      renderUSV(usvData.signals);
+      switchTab('usv');  // BUG1d FIX: switch BEFORE renderUSV so Plotly renders on visible divs
       showNoDataOverlay(false);  // BUG2 FIX: hide overlay when data loaded
-      switchTab('usv');  // BUG1c FIX: auto-switch to USV tab where charts are rendered
+      renderUSV(usvData.signals);
     }
     prog.textContent = 'Chargement AUV…';
     await loadAuvTabs(sortieId);