feat: add global issue search with sidebar button and modal

Add search functionality to quickly find issues by title:
- Backend: add search param (ILIKE) to ListIssues query
- Frontend: search modal using CommandDialog with skeleton loading
- Sidebar: ghost-style search button next to create issue button
- Handle CJK input method composition to avoid premature searches
- Responsive max-height for small screens

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/shared/api/client.ts

@@ -163,6 +163,7 @@ export class ApiClient {
     if (params?.status) search.set("status", params.status);
     if (params?.priority) search.set("priority", params.priority);
     if (params?.assignee_id) search.set("assignee_id", params.assignee_id);
+    if (params?.search) search.set("search", params.search);
     return this.fetch(`/api/issues?${search}`);
   }