Fix created_at > updated_at for API-synced tasks

Use updated_at as fallback for created_at when no existing row,
so API tasks have created_at <= updated_at.

src/infrastructure/db.rs

@@ -140,7 +140,9 @@ impl Db {
             task.position
         };
 
-        // Preserve existing created_at if the task already exists
+        // Preserve existing created_at if the task already exists.
+        // For new tasks from API, use updated_at as created_at proxy
+        // (Google Tasks API does not provide a creation timestamp).
         let created_at = task.created_at.unwrap_or_else(|| {
             conn.query_row(
                 "SELECT created_at FROM tasks WHERE id = ?1",
@@ -149,6 +151,7 @@ impl Db {
             )
             .ok()
             .and_then(|s| NaiveDateTime::parse_from_str(&s, "%Y-%m-%d %H:%M:%S").ok())
+            .or_else(|| task.updated_at)
             .unwrap_or_else(|| chrono::Utc::now().naive_utc())
         });