fix: restore LLM profile test connectivity buttons (lost from git)

Frontend test functionality was implemented but never committed to git.
Re-adds:
- profiles.js: testCard(), testForm(), _showTestResult(), test btn in renderCard
- api.js: testProfile(id) and probeConnectivity(body) methods
- index.html: 测试连通性 button + result div in profile form
- app.css: .btn-test and .profile-test-result styles

Backend /probe and /{id}/test endpoints were already present in llm_profiles.py.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

webapp/static/css/app.css

@@ -294,6 +294,21 @@ table.group-table td { border-bottom: 1px solid #f1f5f9; font-variant-numeric: t
 .btn-sm { padding: 4px 10px; font-size: 12px; }
 .btn-danger { color: var(--bad); border-color: var(--bad); }
 .btn-danger:hover { background: #fee2e2; }
+.btn-test { color: #0369a1; border-color: #0369a1; }
+.btn-test:hover { background: #e0f2fe; }
+
+/* LLM 连通性测试结果 */
+.profile-test-result {
+  margin-top: 8px;
+  padding: 6px 10px;
+  border-radius: 6px;
+  font-size: 12px;
+  font-weight: 500;
+  display: none;
+}
+.profile-test-result:not([hidden]) { display: block; }
+.profile-test-result.ok  { background: #dcfce7; color: #166534; border: 1px solid #bbf7d0; }
+.profile-test-result.fail { background: #fee2e2; color: #991b1b; border: 1px solid #fecaca; word-break: break-all; }
 
 /* 选中态 run 卡片 */
 .run-card.selected {