Improve case-not-found error: show clear message with create button

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/static/index.html

@@ -741,7 +741,15 @@ async function loadCaseView(caseNumber) {
       document.getElementById('caseDocsList').innerHTML = html;
     }
   } catch (e) {
-    document.getElementById('caseViewTitle').textContent = 'שגיאה בטעינת תיק';
+    document.getElementById('caseViewTitle').textContent = `תיק ${caseNumber} לא נמצא`;
+    document.getElementById('caseViewMeta').innerHTML = '';
+    document.getElementById('caseViewLinks').innerHTML = '';
+    document.getElementById('caseDocsList').innerHTML = `
+      <div class="empty">
+        התיק לא קיים עדיין במערכת.<br>
+        <button class="btn btn-primary" style="margin-top:12px" onclick="navigate('/new')">צור תיק חדש</button>
+      </div>`;
+    return;
   }
 
   setupCaseUpload(caseNumber);