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>

server/pkg/db/queries/issue.sql

@@ -4,6 +4,7 @@ WHERE workspace_id = $1
   AND (sqlc.narg('status')::text IS NULL OR status = sqlc.narg('status'))
   AND (sqlc.narg('priority')::text IS NULL OR priority = sqlc.narg('priority'))
   AND (sqlc.narg('assignee_id')::uuid IS NULL OR assignee_id = sqlc.narg('assignee_id'))
+  AND (sqlc.narg('search')::text IS NULL OR title ILIKE '%' || sqlc.narg('search') || '%')
 ORDER BY position ASC, created_at DESC
 LIMIT $2 OFFSET $3;