grammar+db: 3g — RETURNING on INSERT/UPDATE/DELETE (ADR-0033 §5)

Shared RETURNING_CLAUSE (reuses Phase-2 PROJECTION_LIST, now
pub(crate)) as an optional tail on all three SQL DML shapes.
`returning: bool` on the Command variants, set by the ast-builders
and threaded to the worker. run_returning collects the returned rows
as a DataResult (RETURNING mutates + yields in one pass), reusing
resolve_select_column_types for bare-column type recovery; computed
projections stay typeless. DeleteResult gains a `data` field rendered
alongside the cascade summary.

Follow-set fix: `returning` is added to the table-source and
projection bare-alias follow-sets so an INSERT … SELECT row source
stops before RETURNING instead of reading it as a table alias.

Auto-fill × RETURNING: build_sql_insert stops row_source before the
RETURNING token (keeping it preparable for shortid materialisation),
and plan_shortid_autofill re-appends the RETURNING tail so generated
shortids surface in RETURNING *.

Tests (+17): grammar accept on all three; INSERT/UPDATE/DELETE
RETURNING incl. *, aliases, multi-row, type recovery + computed-
typeless; auto-fill × RETURNING (single + multi-row distinct ids);
INSERT…SELECT…RETURNING execution; UPDATE…RETURNING zero-match;
DELETE…RETURNING cascade+rows; app-level render of both. Dev
sql_insert/sql_update/sql_delete entry words still removed in 3j.
1562 pass / 0 fail / 1 ignored. Clippy clean.

src/dsl/grammar/sql_update.rs

@@ -15,7 +15,7 @@
 //! written (ADR-0030 §12). `RETURNING` (3g) lands later.
 
 use crate::dsl::grammar::sql_expr;
-use crate::dsl::grammar::sql_select::{WHERE_CLAUSE, reject_internal_table};
+use crate::dsl::grammar::sql_select::{RETURNING_CLAUSE, WHERE_CLAUSE, reject_internal_table};
 use crate::dsl::grammar::{IdentSource, Node, Word};
 
 static COMMA: Node = Node::Punct(',');
@@ -79,6 +79,7 @@ static SQL_UPDATE_TAIL_NODES: &[Node] = &[
     Node::Word(Word::keyword("set")),
     ASSIGNMENT_LIST,
     Node::Optional(&WHERE_CLAUSE),
+    Node::Optional(&RETURNING_CLAUSE),
     Node::Optional(&Node::Punct(';')),
 ];
 
@@ -153,6 +154,14 @@ mod tests {
         good("t set v = (select max(other) from other_table) where id = 1");
     }
 
+    #[test]
+    fn returning_tail_admitted() {
+        // 3g: optional RETURNING projection_list tail.
+        good("t set v = 1 where id = 1 returning *");
+        good("t set v = 1 returning id, v");
+        good("t set v = 1 where id = 1 returning v as new_v;");
+    }
+
     #[test]
     fn internal_target_table_rejected() {
         bad("__rdbms_playground_columns set a = 1");