feat: ADR-0036 Phase 3b — live typed-slot hints + highlighting for INSERT VALUES

Give each positional INSERT VALUES position its column identity so a lone
literal gets the column-typed slot (live per-column hint + mismatch
highlight) and any expression falls through to sql_expr — completing the
typed-DML-values feature for the INSERT surface (single/multi-row, Form A
and Form B).

New zero-width Node::SetColumn(&TableColumn) primitive establishes the
active column for the value position that follows (sets current_column +
pending_value_column, like an Ident{writes_column} but without consuming
input); a DynamicSubgrammar emits SetColumn(col) + the shared SET_VALUE
per position. Column mapping mirrors do_sql_insert: Form A → listed
columns; Form B → all columns in declaration order (advanced-mode Form B
auto-fills nothing; an omitted shortid in Form A is auto-filled and has no
VALUES position).

Reconcile with the per-tuple arity diagnostic (ADR-0033 §8.1): a
fixed-length typed Seq would reject wrong-arity tuples and suppress that
post-walk diagnostic, so the tuple value list is an arity-gating lookahead
— a correct-arity tuple uses the typed Seq; a wrong-arity tuple keeps the
type-blind sql_expr repeat so §8.1 fires unchanged. Correct-arity tuples
get full live feedback, including a wrong-kind literal like 'text' into an
int column.

Records ADR-0036 Amendment 1 (Phase 3b detail + the arity reconciliation);
ADR-0036 is now fully implemented.

Tests: 1947 passing (+8), 0 failed, 0 skipped, 1 ignored; clippy clean.

src/dsl/grammar/mod.rs

@@ -375,6 +375,25 @@ pub enum Node {
     /// type-awareness). Not memoized: the output depends on the
     /// source, not just `ctx`.
     Lookahead(fn(&WalkContext, &str, usize) -> Self),
+    /// Zero-width node that *establishes the active column* for the
+    /// value slot that follows it (ADR-0036 Phase 3b). Matches the
+    /// empty string and, as a side effect, sets
+    /// `WalkContext::current_column` to the referenced column and
+    /// `pending_value_column` to its name — exactly as an
+    /// `Ident { writes_column: true }` does, but without consuming a
+    /// column identifier from the input.
+    ///
+    /// This is the primitive that gives `INSERT … VALUES (…)`
+    /// positions a per-position column identity: the positions are
+    /// positional (no per-position column ident to write
+    /// `current_column`), so a `DynamicSubgrammar` factory
+    /// (`sql_insert::sql_value_list`) emits `SetColumn(colᵢ)` before
+    /// each value position, then the shared boundary-aware `SET_VALUE`
+    /// slot routes a lone literal to that column's typed slot and any
+    /// expression to `sql_expr`. The referenced `TableColumn` is
+    /// leaked by the factory (bounded by the column count, like the
+    /// `DynamicSubgrammar` `Box::leak`).
+    SetColumn(&'static crate::completion::TableColumn),
     /// Typed value-literal slot (ADR-0024 §Phase D §typed-value-slots).
     ///
     /// Walks `inner` to consume the literal but records the