refactor: rename ColumnName → FieldColumnName

Disambiguates from metaquery.Column.Name (the column's actual name on a
query) — same identifier was overloaded for two unrelated concepts.
FieldColumnName makes the input direction (struct field → column) clear
at the call site.

No deprecation alias: the previous name shipped in v1.1.0 only hours
ago, well before realistic consumer adoption.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Nthalk

metaquery/mqsqlite/scan.go

@@ -167,8 +167,8 @@ func scanRowInto[T any](rows *sql.Rows) (T, error) {
 }
 
 // buildFieldIndex maps column names (from `db` tag or snake_case of the Go
-// field name) to the field's index in t. Uses metaquery.ColumnName so Scan
-// and Validate agree on the name resolution.
+// field name) to the field's index in t. Uses metaquery.FieldColumnName so
+// Scan and Validate agree on the name resolution.
 func buildFieldIndex(t reflect.Type) map[string]int {
 	for t.Kind() == reflect.Pointer {
 		t = t.Elem()
@@ -179,7 +179,7 @@ func buildFieldIndex(t reflect.Type) map[string]int {
 		if !f.IsExported() {
 			continue
 		}
-		name := metaquery.ColumnName(f)
+		name := metaquery.FieldColumnName(f)
 		if name == "-" {
 			continue
 		}

metaquery/validate.go

@@ -47,7 +47,7 @@ func validateShape(t reflect.Type, cols []Column) error {
 		if !f.IsExported() {
 			continue
 		}
-		name := ColumnName(f)
+		name := FieldColumnName(f)
 		if name == "-" {
 			continue
 		}
@@ -77,13 +77,14 @@ func validateShape(t reflect.Type, cols []Column) error {
 	return fmt.Errorf("metaquery: Validate[%s] shape mismatch: %s", t.Name(), strings.Join(all, "; "))
 }
 
-// ColumnName returns the column name a struct field should match against
-// when scanning rows: the `db` tag if set, otherwise snake_case of the Go
-// name. A `db:"-"` tag is returned verbatim so callers can skip the field.
+// FieldColumnName returns the column name a struct field should match
+// against when scanning rows: the `db` tag if set, otherwise snake_case of
+// the Go name. A `db:"-"` tag is returned verbatim so callers can skip the
+// field.
 //
 // Exported so adapters (mqpgx, mqsqlite, future ones) and Validate share
 // one source of truth for the field-to-column convention.
-func ColumnName(f reflect.StructField) string {
+func FieldColumnName(f reflect.StructField) string {
 	if tag, ok := f.Tag.Lookup("db"); ok {
 		if comma := strings.IndexByte(tag, ','); comma >= 0 {
 			tag = tag[:comma]