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.

Inizia dal punto di ingresso CLI plugin marketplace browse <name> e confronta l’output attuale come lista piatta con i workflow di ricerca descritti nell’issue. Decidi se il comportamento completato debba essere una ricerca interattiva, un flag --search o entrambi, quindi verifica il filtraggio con gli esempi awesome-copilot e copilot-plugins e con ricerche come sql, github e lsp.