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_dml_e2e.rs

@@ -149,7 +149,7 @@ fn seed(db: &Database, rt: &tokio::runtime::Runtime, sql: &str) {
 }
 
 fn query(db: &Database, rt: &tokio::runtime::Runtime, table: &str) -> Vec<Vec<Option<String>>> {
-    rt.block_on(db.query_data(table.to_string(), None, None, None))
+    rt.block_on(db.query_data(table.to_string(), None, None))
         .unwrap_or_else(|e| panic!("query_data {table}: {e:?}"))
         .rows
 }