refactor(db): unwind vestigial worker source plumbing (ADR-0052 follow-up)

ADR-0052 moved success journaling out of the worker to the dispatch
layer, leaving the `source` that handlers threaded purely for the
worker's old history.log write dead. Remove it:

- drop `_source` from finalize_persistence and do_rebuild_from_text
- inline + delete the three read-only *_request wrappers
- drop the now-unused `source` param from the ~30 forwarding worker
  handlers (leaf + composite), compiler-guided
- remove the `source` field from the DescribeTable/QueryData/RunSelect
  requests and their DatabaseHandle methods (call sites updated)

The only worker `source` left is the snapshot/undo label
(snapshot_then / stage_pre_mutation / begin_batch). Purely mechanical,
no behaviour change. 2471 pass / 0 fail / 1 ignored, clippy clean.

tests/it/undo_snapshots.rs

@@ -63,7 +63,7 @@ async fn insert_named(db: &Database, name: &str) {
 }
 
 async fn row_count(db: &Database) -> usize {
-    db.query_data("Customers".to_string(), None, None, None)
+    db.query_data("Customers".to_string(), None, None)
         .await
         .unwrap()
         .rows
@@ -306,7 +306,7 @@ async fn sql_delete(db: &Database, input: &str) {
 }
 
 async fn count_t(db: &Database) -> usize {
-    db.query_data("T".to_string(), None, None, None)
+    db.query_data("T".to_string(), None, None)
         .await
         .unwrap()
         .rows
@@ -378,7 +378,7 @@ fn undo_restores_db_and_csv_consistently() {
         // Both the database read model and the on-disk CSV are
         // restored — the (db, csv) pair stays consistent.
         assert_eq!(
-            db.query_data("T".to_string(), None, None, None)
+            db.query_data("T".to_string(), None, None)
                 .await
                 .unwrap()
                 .rows