command: Operand carries a source span

Each WHERE-expression Operand now records the byte span of the
terminal it was built from — the precise per-literal highlight
target for an expression WARNING (finishing ADR-0027 §2's
highlight/hint wiring). parse_operand captures MatchedItem::span;
the RowFilter::eq convenience constructor uses Operand::NO_SPAN.

PartialEq is hand-written to ignore the span — it is editor
metadata, so Command equality stays whitespace- and
position-independent, which the Expr test corpus relies on.
No behaviour change; 1100 tests still pass, clippy clean.

src/db.rs

@@ -4251,8 +4251,8 @@ fn compile_operand(
     params: &mut Vec<rusqlite::types::Value>,
 ) -> String {
     match operand {
-        Operand::Column(name) => quote_ident(name),
-        Operand::Literal(value) => {
+        Operand::Column { name, .. } => quote_ident(name),
+        Operand::Literal { value, .. } => {
             params.push(bind_where_literal(value, against));
             format!("?{}", params.len())
         }
@@ -4264,12 +4264,12 @@ fn compile_operand(
 /// yield `None`.
 fn operand_column_type(operand: &Operand, schema: &ReadSchema) -> Option<Type> {
     match operand {
-        Operand::Column(name) => schema
+        Operand::Column { name, .. } => schema
             .columns
             .iter()
             .find(|c| c.name.eq_ignore_ascii_case(name))
             .and_then(|c| c.user_type),
-        Operand::Literal(_) => None,
+        Operand::Literal { .. } => None,
     }
 }