[codex] Remove redundant plugin app auth state (#27465)

## Summary

- remove the redundant `needsAuth` field from `AppSummary` and generated
app-server schemas
- stop `plugin/read` from querying Apps MCP solely to hydrate unused
connector auth state
- preserve `plugin/install.appsNeedingAuth` membership and
`app/list.isAccessible` as the authentication signals

## Why

Codex App and TUI do not consume `plugin/read.plugin.apps[].needsAuth`.
Hydrating it could establish an Apps MCP connection and discover tools
on a cold `plugin/read` request, adding avoidable latency. The plugin
APIs are still marked under development, so removing this wire field is
preferable to retaining a misleading default.

## Verification

- `just write-app-server-schema`
- `just fmt`
- `just test -p codex-app-server-protocol`
- `just test -p codex-app-server
plugin_install_uses_remote_apps_needing_auth_response`
- `just test -p codex-app-server
plugin_install_returns_apps_needing_auth`
- `just test -p codex-app-server
plugin_read_returns_plugin_details_with_bundle_contents`
- `just test -p codex-tui
plugin_detail_popup_snapshot_shows_install_actions_and_capability_summaries`
- `$xin-build` simplify and debug reviews

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -711,15 +711,11 @@
         },
         "name": {
           "type": "string"
-        },
-        "needsAuth": {
-          "type": "boolean"
         }
       },
       "required": [
         "id",
-        "name",
-        "needsAuth"
+        "name"
       ],
       "type": "object"
     },