feat: add instructional text to cookie picker page

"Select the domains of cookies you want to import to GStack Browser.
You'll be able to browse those sites with the same login as your
other browser."

Also fixes stale test that expected hardcoded '--model', 'opus'.

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

browse/src/cookie-picker-ui.ts

@@ -46,6 +46,15 @@ export function getCookiePickerHTML(serverPort: number, authToken?: string): str
     font-family: 'SF Mono', 'Fira Code', monospace;
   }
 
+  .subtitle {
+    padding: 10px 24px 12px;
+    font-size: 13px;
+    color: #999;
+    line-height: 1.5;
+    border-bottom: 1px solid #222;
+    background: #0f0f0f;
+  }
+
   /* ─── Layout ──────────────────────────── */
   .container {
     display: flex;
@@ -300,6 +309,8 @@ export function getCookiePickerHTML(serverPort: number, authToken?: string): str
   <span class="port">localhost:${serverPort}</span>
 </div>
 
+<p class="subtitle">Select the domains of cookies you want to import to GStack Browser. You'll be able to browse those sites with the same login as your other browser.</p>
+
 <div id="banner" class="banner"></div>
 
 <div class="container">

browse/test/sidebar-security.test.ts

@@ -86,9 +86,11 @@ describe('Sidebar prompt injection defense', () => {
 
   // --- Model Selection ---
 
-  test('default model is opus', () => {
-    // The args array should include --model opus
-    expect(SERVER_SRC).toContain("'--model', 'opus'");
+  test('model routing defaults to opus for analysis tasks', () => {
+    // pickSidebarModel returns opus for ambiguous/analysis messages
+    expect(SERVER_SRC).toContain("return 'opus'");
+    // spawnClaude uses the model router
+    expect(SERVER_SRC).toContain("'--model', model");
   });
 
   // --- Trust Boundary ---