fix: SSE 实时更新同步状态指示器

sync-status 区域未包含在 SSE OOB swap 中，导致页面加载后
状态永远不会更新。新增 SyncStatusPartial 模板并加入 SSE
payload，使 dirty count 归零时 UI 能实时切换。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/web/sse.rs

@@ -119,6 +119,10 @@ fn render_sse_payload(
         webdav_running: status.webdav_running,
     };
 
+    let sync_status = SyncStatusPartial {
+        all_synced: status.all_synced,
+    };
+
     let mut html = String::new();
     // Primary target: dashboard stats
     if let Ok(s) = stats.render() {
@@ -132,6 +136,10 @@ fn render_sse_payload(
     if let Ok(s) = badges.render() {
         html.push_str(&s);
     }
+    // OOB: sync status indicator
+    if let Ok(s) = sync_status.render() {
+        html.push_str(&s);
+    }
     html
 }
 
@@ -205,3 +213,9 @@ struct ProtocolBadgesPartial {
     nfs_exported: bool,
     webdav_running: bool,
 }
+
+#[derive(Template)]
+#[template(path = "web/partials/sync_status.html")]
+struct SyncStatusPartial {
+    all_synced: bool,
+}

templates/web/partials/sync_status.html

@@ -0,0 +1,13 @@
+{% if all_synced %}
+<div class="sync-indicator sync-ok" id="sync-status" hx-swap-oob="outerHTML:#sync-status">
+  <span class="sync-icon">✓</span>
+  <span class="sync-text">已全部同步 — 可以断网</span>
+  <span class="sync-sub">All synced — safe to disconnect</span>
+</div>
+{% else %}
+<div class="sync-indicator sync-pending" id="sync-status" hx-swap-oob="outerHTML:#sync-status">
+  <span class="sync-icon">⏳</span>
+  <span class="sync-text">同步进行中 — 请勿断网</span>
+  <span class="sync-sub">Sync in progress — do not disconnect</span>
+</div>
+{% endif %}