grammar+db: 3e — SQL UPDATE grammar + execution (ADR-0033 §2)

New src/dsl/grammar/sql_update.rs: SQL_UPDATE_SHAPE =
<table> SET col = sql_expr (',' …)* [WHERE sql_expr] [';'], the
__rdbms_* target rejection, and the shared sql_expr on both the
assignment RHS and the predicate. No --all-rows rail — a SQL
UPDATE without WHERE runs as written (ADR-0030 §12). Reuses
sql_select::WHERE_CLAUSE (now pub(crate)) so the predicate
diagnostics are identical. The target uses the shared `table_name`
ident role (not a bespoke one) so the Phase-2 schema-existence and
predicate-warning passes collect it as a scope binding and check
the SET / WHERE columns for free — a bespoke role left them
unchecked (the cross-cut tests caught this).

Command::SqlUpdate { sql, target_table }; Request::RunSqlUpdate +
do_sql_update (execute validated SQL via execute_with_fk_enrichment,
re-persist the target CSV, append history.log). 3e surfaces the
affected-row count only; precise row output is RETURNING (3g), so
the update-success render skips a column-less data set rather than
showing a misleading "(no rows)" band. Behind the dev `sql_update`
entry word until 3j.

Tests: grammar accept/reject; integration (single/multi-col,
no-WHERE all-rows, sql_expr in SET, scalar subquery in SET,
zero-match success, history); walker cross-cut (unknown SET column
→ unknown_column, `= NULL` in WHERE → eq_null warning); app-level
render-guard both ways (column-less → count only; with columns →
table renders). 1524 green, clippy clean.

src/dsl/grammar/mod.rs

@@ -30,6 +30,7 @@ pub mod shared;
 pub mod sql_expr;
 pub mod sql_insert;
 pub mod sql_select;
+pub mod sql_update;
 
 use crate::dsl::command::Command;
 use crate::dsl::walker::context::WalkContext;
@@ -575,6 +576,10 @@ pub static REGISTRY: &[(&CommandNode, CommandCategory)] = &[
     // temporary `sqlinsert` entry word keeps it isolated from the
     // DSL `insert` word until 3j wires the shared entry.
     (&data::SQL_INSERT, CommandCategory::Advanced),
+    // SQL UPDATE development scaffold (sub-phase 3e); the temporary
+    // `sql_update` entry word keeps it isolated from the DSL
+    // `update` word until 3j wires the shared entry.
+    (&data::SQL_UPDATE, CommandCategory::Advanced),
 ];
 
 /// Whether `entry` names an advanced-mode-only command (ADR-0030