feat(library): add lyrics filtering and metadata actions

lib/utils/isrc_utils.dart

@@ -0,0 +1,27 @@
+final RegExp _canonicalIsrcPattern = RegExp(r'^[A-Z]{2}[A-Z0-9]{3}\d{7}$');
+
+String normalizeIsrc(String? value) =>
+    (value ?? '').trim().toUpperCase().replaceAll(RegExp(r'[-\s]'), '');
+
+/// Returns the compact canonical value only when [value] is a valid ISRC.
+/// Invalid provider/tag values remain visible and copyable without mutation.
+String canonicalIsrcForCopy(String? value) {
+  final original = value?.trim() ?? '';
+  final normalized = normalizeIsrc(original);
+  return _canonicalIsrcPattern.hasMatch(normalized) ? normalized : original;
+}
+
+/// Formats a valid canonical ISRC for display without changing stored tags.
+///
+/// Example: `AA9BQ2200061` becomes `AA-9BQ-22-00061`.
+String formatIsrcForDisplay(String? value) {
+  final original = value?.trim() ?? '';
+  final canonical = canonicalIsrcForCopy(original);
+  if (!_canonicalIsrcPattern.hasMatch(canonical)) {
+    return original;
+  }
+  return '${canonical.substring(0, 2)}-'
+      '${canonical.substring(2, 5)}-'
+      '${canonical.substring(5, 7)}-'
+      '${canonical.substring(7)}';
+}

lib/utils/ordered_range_selection.dart

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+/// Adds every visible item between [anchor] and [target] to [selected].
+///
+/// Dart's default [Set] preserves insertion order, so walking backwards also
+/// preserves the direction chosen by the user when results are later copied,
+/// shared, or batch processed.
+T addOrderedSelectionRange<T>({
+  required Set<T> selected,
+  required List<T> visibleItems,
+  required T target,
+  T? anchor,
+}) {
+  final anchorIndex = anchor == null ? -1 : visibleItems.indexOf(anchor);
+  final targetIndex = visibleItems.indexOf(target);
+  if (anchorIndex < 0 || targetIndex < 0) {
+    selected.add(target);
+    return target;
+  }
+
+  final step = targetIndex >= anchorIndex ? 1 : -1;
+  for (var index = anchorIndex; ; index += step) {
+    selected.add(visibleItems[index]);
+    if (index == targetIndex) break;
+  }
+  return target;
+}
+
+/// Toggles one item and returns the next range-selection anchor.
+T? toggleOrderedSelection<T>({required Set<T> selected, required T target}) {
+  if (selected.add(target)) return target;
+  selected.remove(target);
+  return selected.isEmpty ? null : selected.last;
+}