fix: atomic ingestion persist with task reclaim and shared cleanup.

One transaction per task replaces prior artifact rows; workers skip the pipeline when content already exists, eval seeding reuses persist_artifacts, and deletes clear graph children via shared SQL.

common/src/storage/db.rs

@@ -150,7 +150,7 @@ impl SurrealDbClient {
 
     /// Upsert an object in SurrealDB, replacing any existing record with the same ID.
     ///
-    /// Useful for idempotent ingestion flows.
+    /// Useful when a single record should be replaced by id (admin updates, embedding rows, etc.).
     ///
     /// # Errors
     ///