test(frontend): cover NewSessionDialog model degradation + invalidate sessions on resume

- Add NewSessionDialog.test.tsx covering §9 graceful degradation:
  empty models -> free-text input; non-empty models -> dropdown; plus a
  createSession body-keys assertion
- Normalize model entries to {value,label} so object-shaped models
  ({provider,id}) render correctly in the dropdown (was assuming strings)
- NavSessions: invalidate the ["sessions"] query after a successful
  resumeSession so the list/status refreshes immediately

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/NewSessionDialog.tsx

@@ -38,8 +38,18 @@ export function NewSessionDialog({ onCreated }: Props) {
     enabled: open,
   });
 
-  const modelList: string[] = Array.isArray(modelsData?.models)
-    ? (modelsData.models as string[])
+  // Model entries may be plain strings or objects ({ id, provider, ... });
+  // normalize to { value, label } so the dropdown renders either shape.
+  const modelList: { value: string; label: string }[] = Array.isArray(
+    modelsData?.models,
+  )
+    ? modelsData.models.map((m) => {
+        if (typeof m === "string") return { value: m, label: m };
+        const o = m as { id?: string; provider?: string };
+        const value = o.id ?? "";
+        const label = o.provider ? `${o.provider}/${value}` : value;
+        return { value, label };
+      })
     : [];
 
   // When workspace list loads, pre-select the first one if nothing chosen yet
@@ -140,8 +150,8 @@ export function NewSessionDialog({ onCreated }: Props) {
               >
                 <option value="">— default —</option>
                 {modelList.map((m) => (
-                  <option key={m} value={m}>
-                    {m}
+                  <option key={m.value} value={m.value}>
+                    {m.label}
                   </option>
                 ))}
               </select>