feat: ADR-0035 4h — ALTER TABLE … RENAME TO

The one genuinely new low-level op in Phase 4: a native engine RENAME TO
plus one-transaction reconciliation (commit-db-last) of everything the
engine does not track —

- every metadata row naming the table: __rdbms_playground_columns, both
  ends of __rdbms_playground_relationships (FK parent, child, and
  self-referential), and __rdbms_playground_table_checks;
- the CSV file, via the existing persistence rewrite+delete path
  (rewritten_tables=[new], deleted_tables=[old]) — no new method;
- CHECK text that qualifies a column with the old table name
  (T.age → U.age, column- and table-level): the engine rewrites the live
  CHECK but the stored text would drift and break a fresh rebuild (a
  planning-/runda finding); rewrite_check_table_qualifier keeps them in
  step. Bounded — a CHECK references only its own table.

Grammar: a fifth AlterTableAction (RenameTable { new }), added by
splitting the `rename` verb into one branch with an inner Choice on a
distinct second keyword (column vs to); the new-name slot mirrors the
CREATE TABLE name slot (NewName + reject_internal_table validator).

Refusals are engine-neutral and case-insensitive (the engine matches
names that way): same-name, case-only, existing-target, __rdbms_*, and
non-existent source. Auto-named indexes and relationships keep their
stale names (only table-name columns update — §6 scope). One undo step;
advanced-mode only; closes the rename half of C1.

Tests: 8 Tier-3 e2e + rewrite-helper unit tests + parse-dispatch tests.
Full suite 1903 passing / 0 failing / 1 ignored; clippy clean.

src/app.rs

@@ -1608,6 +1608,12 @@ impl App {
                 AlterTableAction::DropConstraint { .. } => {
                     (Operation::DropConstraint, Some(table.as_str()), None)
                 }
+                // `RENAME TO <new>` — the failure concerns the table being
+                // renamed (the old name); the executor authors the
+                // existing-target / same-name refusals (ADR-0035 §6, 4h).
+                AlterTableAction::RenameTable { .. } => {
+                    (Operation::RenameTable, Some(table.as_str()), None)
+                }
             },
             C::SqlCreateTable { name, .. } => {
                 (Operation::CreateTable, Some(name.as_str()), None)