List Gemini output in Gemini CLI extension gallery

[chubes4]

Parent: #45

Goal

Make the generated Gemini output discoverable through Gemini CLI's official extension gallery path.

Evidence

• Extension gallery: https://geminicli.com/extensions/
• Release/listing docs: https://geminicli.com/docs/extensions/releasing/
• Gemini docs state the gallery automatically indexes public extensions with the gemini-cli-extension GitHub topic and a root gemini-extension.json manifest.
• Generated output: plugins/gemini/.

Tasks

• Decide whether plugins/gemini/ needs a standalone publishable repository or export path before gallery discovery.
• Ensure the publishable artifact has a valid root gemini-extension.json manifest.
• Add the gemini-cli-extension topic to the public repository used for distribution.
• Tag/release as needed and verify it appears in the gallery.
• Record the listing URL/status back in Epic: submit Build with WordPress outputs to official agent marketplaces #45.