add CPSearchTemplate support

[sINFdorako]

Summary

• Add CPSearchTemplate wrapping Apple's CPSearchTemplate API for CarPlay search functionality
• Search results use existing CPListItem — no new item types needed
• Three delegate callbacks bridged to Dart: onSearchTextUpdated, onSearchResultSelected,
  onSearchButtonPressed

Changes

• New: FCPSearchTemplate.swift — Swift wrapper implementing CPSearchTemplateDelegate
• New: search_template.dart — Dart model with callback-based API
• Modified: Plugin entry point, enums, controller, worker, and barrel export to register the new
  template across the full method channel bridge

Usage

CPSearchTemplate(
  onSearchTextUpdated: (searchText, updateResults) {
    final results = await search(searchText);
    updateResults(results.map((r) => CPListItem(text: r.title)).toList());
  },
  onSearchResultSelected: (item, complete) {
    // handle selection
    complete();
  },
  onSearchButtonPressed: () {},
)