Add search/filter support to plugin marketplace browse command

Describe the feature or problem you'd like to solve

When running  copilot plugin marketplace browse  , the output is a long flat list with no way to search or filter. This makes it hard to discover relevant plugins as marketplaces grow

Proposed solution

Add an interactive search input to the  plugin marketplace browse  command — similar to how Claude Code's plugin browser works — that lets users type to filter results in real time. Alternatively, support a  --search  flag:

copilot plugin marketplace browse awesome-copilot --search "sql"

Example prompts or workflows

1. User runs  /plugin marketplace browse awesome-copilot  and types "github" to filter matching plugins
2. User runs  copilot plugin marketplace browse copilot-plugins --search "lsp"  to find LSP-related plugins
3. User presses  /  inside the browse output to enter search mode (fuzzy search)

Additional context

The current UX requires piping to  grep  as a workaround, which is not discoverable or user-friendly. Claude Code's marketplace UI is a good reference for the interactive search experience.

CLI エントリポイント plugin marketplace browse <name> から開始し、現在のフラットリスト形式の出力を、issue で説明されている検索ワークフローと比較します。完成時の動作をインタラクティブ検索、--search フラグ、またはその両方のどれにするべきかを判断し、その後、awesome-copilot と copilot-plugins の例、および sql、github、lsp などの検索でフィルタリングを検証します。