Submit Factory Droid output to Factory plugin marketplace

Parent: #45

## Goal
Submit the generated Build with WordPress Factory Droid output to Factory's plugin marketplace path.

## Evidence
- Official docs: https://docs.factory.ai/cli/configuration/plugins
- Factory documents plugin marketplaces, `/plugins`, and CLI marketplace management.
- Official marketplace: `Factory-AI/factory-plugins`.
- Generated output: `plugins/factory/`.

## Tasks
- Confirm whether submission should target the official `Factory-AI/factory-plugins` marketplace or an Automattic-owned marketplace repo first.
- Validate `plugins/factory/` against Factory's plugin manifest and structure requirements.
- Prepare submission PR or marketplace repository update.
- Record the submission URL/status back in #45.

Start with the Factory plugin documentation at https://docs.factory.ai/cli/configuration/plugins and inspect the generated plugins/factory/ directory against its manifest and structure requirements. Resolve whether Factory-AI/factory-plugins or an Automattic-owned marketplace is the target, then prepare the marketplace submission and record its URL or status in parent issue #45.

Written by the indexing model from the issue text.