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/sql_update.rs

@@ -501,7 +501,7 @@ fn update_all_rows_flag_in_advanced_updates_every_row() {
         "the --all-rows update replays through the DSL fall-back; events: {events:?}"
     );
     let rows = rt
-        .block_on(db.query_data("t".to_string(), None, None, None))
+        .block_on(db.query_data("t".to_string(), None, None))
         .expect("query")
         .rows;
     assert_eq!(rows.len(), 2, "both rows present");