fix: 版本检查 — 后端设置 checked 字段 + 前端 info 合并显示

- UpdateService.status 增加 checked/current_version/latest_version
- _check_version 成功后设置 checked=True
- 设置页 update-notes 合并版本信息和时间戳 (替代 innerHTML 覆盖)

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

static/web_panel/pages/settings.html

@@ -93,12 +93,13 @@
         var r = await fetch("./api/updates"), d = await r.json();
         document.getElementById("ver-current").textContent = d.current_version || d.latest_version || "?";
         var badge = document.getElementById("ver-badge");
+        var notesHtml = "";
         if (d.update_available) {
           badge.textContent = "↻ " + d.latest_version + " 可用";
           badge.style.background = "var(--success,#4caf50)";
           badge.style.color = "#fff";
           document.getElementById("btn-apply").style.display = "inline-block";
-          document.getElementById("update-notes").innerHTML = d.latest_version ? "最新版本: <b>"+esc(d.latest_version)+"</b>" : "";
+          notesHtml = d.latest_version ? "最新版本: <b>"+esc(d.latest_version)+"</b>" : "";
         } else if (d.checked) {
           badge.textContent = "✓ 已是最新";
           badge.style.background = "var(--md-sys-color-surface-container-lowest)";
@@ -108,8 +109,9 @@
           badge.textContent = "⏳ 等待检查...";
         }
         if (d.last_check) {
-          document.getElementById("update-notes").innerHTML += " <span style='font-size:.75rem;color:var(--text-dim)'>上次检查: "+new Date(d.last_check*1000).toLocaleString()+"</span>";
+          notesHtml += (notesHtml ? " | " : "") + "上次检查: "+new Date(d.last_check*1000).toLocaleString();
         }
+        document.getElementById("update-notes").innerHTML = notesHtml;
       } catch(e) {}
     }