[codex] Make plugin details capability aware

[felixxia-oai]

Summary

Makes plugin details/read flows capability-aware so auth-filtered plugin surfaces report the same usable app/MCP/skill shape as the marketplace and install flows.

Validation

Not run; this change was rebased onto the current plugin auth stack and pushed as a draft PR.

Manual test

1. set up a local marketplace with a plugin that has both app and mcp declarations

// .app.json
{
  "apps": {
    "linear": {
      "id": "some_id"
    }
  }
}

// .mcp.json
{
  "mcpServers": {
    "linear": {
      "type": "http",
      "url": "https://mcp.linear.app/mcp",
      "oauth_resource": "https://mcp.linear.app/mcp"
    },
    "linear2": {
      "type": "http",
      "url": "https://mcp.linear2.app/mcp",
      "oauth_resource": "https://mcp.linear2.app/mcp"
    }
  }
}

2a. login in with api key and observe plugin details page which shows no apps (note we don't show "app not available due to api key log in as there's no way to differentiate between no apps and app without substitute mcp exists" without significantly more code changes, i've separated this to a follow up if we want that behaviour.

2b. log in with chat and observe intended conflict resolution logic

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 55973b4a8a

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[xl-openai]

Please cleanup plugin_details_app_summaries_enabled before merge.