Fix sync: CreateList action + server ID mapping

- Added SyncAction::CreateList variant
- create_task returns server Task, added create_list API
- Sync engine processes CreateList first, updates IDs in batch
- After Create/CreateList success, local IDs updated to server IDs

src/infrastructure/db.rs

@@ -281,6 +281,7 @@ impl Db {
             SyncAction::Update => "Update",
             SyncAction::Delete => "Delete",
             SyncAction::Reorder => "Reorder",
+            SyncAction::CreateList => "CreateList",
         };
         let conn = self.conn.lock().unwrap();
         conn.execute(
@@ -306,6 +307,47 @@ impl Db {
         count > 0
     }
 
+    pub fn update_task_id(&self, old_id: &str, new_id: &str) -> SqlResult<()> {
+        let conn = self.conn.lock().unwrap();
+        conn.execute(
+            "UPDATE tasks SET id = ?1 WHERE id = ?2",
+            params![new_id, old_id],
+        )?;
+        Ok(())
+    }
+
+    pub fn update_sync_task_id(&self, old_id: &str, new_id: &str) -> SqlResult<()> {
+        let conn = self.conn.lock().unwrap();
+        conn.execute(
+            "UPDATE sync_queue SET task_id = ?1 WHERE task_id = ?2",
+            params![new_id, old_id],
+        )?;
+        Ok(())
+    }
+
+    pub fn update_list_id(&self, old_id: &str, new_id: &str) -> SqlResult<()> {
+        let conn = self.conn.lock().unwrap();
+        conn.execute(
+            "UPDATE task_lists SET id = ?1 WHERE id = ?2",
+            params![new_id, old_id],
+        )?;
+        conn.execute(
+            "UPDATE tasks SET list_id = ?1 WHERE list_id = ?2",
+            params![new_id, old_id],
+        )?;
+        Ok(())
+    }
+
+    #[allow(dead_code)]
+    pub fn update_sync_list_id(&self, old_id: &str, new_id: &str) -> SqlResult<()> {
+        let conn = self.conn.lock().unwrap();
+        conn.execute(
+            "UPDATE sync_queue SET list_id = ?1 WHERE list_id = ?2",
+            params![new_id, old_id],
+        )?;
+        Ok(())
+    }
+
     pub fn drain_sync(&self) -> Vec<SyncQueueItem> {
         let conn = self.conn.lock().unwrap();
         let items: Vec<SyncQueueItem> = {
@@ -319,6 +361,7 @@ impl Db {
                     "\"Update\"" | "Update" => SyncAction::Update,
                     "\"Delete\"" | "Delete" => SyncAction::Delete,
                     "\"Reorder\"" | "Reorder" => SyncAction::Reorder,
+                    "\"CreateList\"" | "CreateList" => SyncAction::CreateList,
                     _ => SyncAction::Update,
                 };
                 Ok(SyncQueueItem {