Initial plugins TUI menu - list and read only. tui + tui_app_server

[canvrno-oai]

Preliminary /plugins TUI menu

• Adds a preliminary /plugins menu flow in both tui and tui_app_server.
• Fetches plugin list data asynchronously and shows loading/error/cached states.
• Limits this first pass to the curated ChatGPT marketplace.
• Shows available plugins with installed/status metadata.
• Supports in-menu search over plugin display name, plugin id, plugin name, and marketplace label.
• Opens a plugin detail view on selection, including summaries for Skills, Apps, and MCP Servers, with back navigation.

Testing

• Launch codex-cli with plugins enabled (--enable plugins).
• Run /plugins and verify:
  • loading state appears first
  • plugin list is shown
  • search filters results
  • selecting a plugin opens detail view, with a list of skills/connectors/MCP servers for the plugin
  • back action returns to the list.
• Verify disabled behavior by running /plugins without plugins enabled (shows “Plugins are disabled” message).
• Launch with --enable tui_app_server (and plugins enabled) and repeat the same /plugins flow; behavior should match.