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/iteration3_rebuild.rs

@@ -76,7 +76,7 @@ fn rebuild_restores_schema_only_project() {
 
     // Phase 4: confirm Customers exists with the right shape.
     let desc = rt()
-        .block_on(async { db.describe_table("Customers".to_string(), None).await })
+        .block_on(async { db.describe_table("Customers".to_string()).await })
         .expect("describe_table");
     assert_eq!(desc.name, "Customers");
     let cols: Vec<&str> = desc.columns.iter().map(|c| c.name.as_str()).collect();
@@ -143,7 +143,7 @@ fn rebuild_restores_rows_from_csv() {
     });
 
     let rows = rt()
-        .block_on(async { db.query_data("Customers".to_string(), None, None, None).await })
+        .block_on(async { db.query_data("Customers".to_string(), None, None).await })
         .expect("query_data");
     assert_eq!(rows.rows.len(), 2);
     let names: Vec<Option<String>> = rows.rows.iter().map(|r| r[1].clone()).collect();
@@ -371,7 +371,7 @@ fn rebuild_preserves_created_at_from_yaml() {
     // Trigger any successful command so project.yaml is
     // rewritten from the now-rebuilt db state.
     rt().block_on(async {
-        db.describe_table("T".to_string(), Some("show table T".to_string()))
+        db.describe_table("T".to_string())
             .await
             .unwrap();
         // describe is read-only; force a rewrite by adding a column.
@@ -451,7 +451,7 @@ fn rebuild_restores_indexes() {
     });
 
     let desc = rt()
-        .block_on(async { db.describe_table("Customers".to_string(), None).await })
+        .block_on(async { db.describe_table("Customers".to_string()).await })
         .expect("describe_table");
     assert_eq!(desc.indexes.len(), 1, "index should survive rebuild");
     assert_eq!(desc.indexes[0].name, "idx_email");