fix: correct visual regressions and UX gaps from review

- Remove double border-top separator on evaluation-summary-section
- Add overflow: hidden to competence-card to contain header negative margins
- Replace removed --shadow-lg with --shadow-card-hover in .dragging rule
- Add htmlFor/id pairing on checkbox and label for click accessibility
- Show error toast when PDF export attempted with no observation generated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/Bilan.css

@@ -392,6 +392,7 @@
   display: flex;
   flex-direction: column;
   gap: 16px;
+  overflow: hidden;
 }
 
 .competence-card h4 {
@@ -476,7 +477,7 @@
   background: var(--color-indigo-50);
   border-color: var(--color-indigo-500);
   border-style: dashed;
-  box-shadow: var(--shadow-lg);
+  box-shadow: var(--shadow-card-hover);
 }
 
 .competence-item .competence-label {
@@ -710,8 +711,7 @@
 /* Restructured summary and evaluation output section */
 .evaluation-summary-section {
   margin-top: 40px;
-  border-top: 1px dashed var(--border-slate-200);
-  padding-top: 32px;
+  padding-top: 0;
   text-align: left;
 }
 

src/components/Bilan.jsx

@@ -696,7 +696,10 @@ ${notesFormateur}`,
 
   const downloadPDF = useCallback(async () => {
     const textRaw = observation.trim();
-    if (!textRaw) return;
+    if (!textRaw) {
+      showStatus("Génère d'abord un bilan avant d'exporter le PDF.", "error");
+      return;
+    }
 
     try {
       showStatus("Préparation du PDF…", "info", true);
@@ -1047,6 +1050,7 @@ ${notesFormateur}`,
                       onDragEnd={handleDragEnd}
                     >
                       <input
+                        id={`check-${item.id}`}
                         type="checkbox"
                         className="competence-checkbox sel"
                         checked={item.checked}
@@ -1054,7 +1058,7 @@ ${notesFormateur}`,
                           updateItem(item.id, { checked: event.target.checked })
                         }
                       />
-                      <label className="competence-label">
+                      <label className="competence-label" htmlFor={`check-${item.id}`}>
                         <div>{item.label}</div>
                       </label>
                       <div