feat: add sync checkpoint restore for last successful sync

Capture rolling online DB snapshots after push/drain/reconcile and expose SyncPage 数据恢复 plus checkpoint/restore APIs; mark Z12h and restore done in coop docs.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/api.ts

@@ -1063,6 +1063,55 @@ export async function reconcileSyncChannel(session: Session, id: string) {
   };
 }
 
+export type SyncCheckpointSlot = {
+  synced_at?: string;
+  source?: string;
+  table_count?: number;
+  row_count?: number;
+};
+
+export type SyncCheckpointMeta = {
+  channel_id?: string;
+  latest?: SyncCheckpointSlot | null;
+  previous?: SyncCheckpointSlot | null;
+};
+
+export async function getSyncCheckpointMeta(session: Session, id: string) {
+  const res = await apiFetch(`/api/v1/admin/sync/channels/${encodeURIComponent(id)}/checkpoint`, {
+    headers: { Authorization: `Bearer ${session.accessToken}` },
+  });
+  const data = await readJson(res);
+  throwIfBad(res, data, "get checkpoint failed");
+  return data as SyncCheckpointMeta;
+}
+
+export async function restoreSyncChannel(
+  session: Session,
+  id: string,
+  body: { which?: "latest" | "previous"; confirm: boolean }
+) {
+  const res = await apiFetch(`/api/v1/admin/sync/channels/${encodeURIComponent(id)}/restore`, {
+    method: "POST",
+    headers: {
+      Authorization: `Bearer ${session.accessToken}`,
+      "Content-Type": "application/json",
+    },
+    body: JSON.stringify(body),
+  });
+  const data = await readJson(res);
+  throwIfBad(res, data, "restore failed");
+  return data as {
+    ok?: boolean;
+    which?: string;
+    synced_at?: string;
+    source?: string;
+    tables?: number;
+    upserted?: number;
+    deleted?: number;
+    restored_at?: string;
+  };
+}
+
 /** 外部源 C → 写入本地 B，再经 outbox 同步到线上 A */
 export async function ingestSyncRows(
   session: Session,