feat(skills): default plugin creator to personal share flow

[efrazer-oai]

Summary

Plugin creation now defaults to the personal marketplace path and ends with a readable handoff back into Codex after a marketplace-backed scaffold.

Before this change, plugin-creator centered repo-local marketplace updates and did not clearly guide the agent to return the user to the created plugin afterward. This PR updates the bundled system skill so marketplace-backed scaffolds default to ~/plugins/<plugin-name> plus ~/.agents/plugins/marketplace.json, ask for user intent only when an existing repo marketplace makes personal vs team scope ambiguous, and end with named Markdown deeplinks labeled View <plugin-name> and Share <plugin-name>.

What changed

• default marketplace-backed creation to the personal plugin location
• document the explicit repo/team override path for codebases that should own the plugin entry
• ask personal vs team only when the current Git repo already has .agents/plugins/marketplace.json and the user has not stated scope
• require named Markdown deeplinks after marketplace-backed creation so the final response returns the user to the exact plugin cleanly
• keep the deeplink targets precise with real absolute marketplacePath and normalized pluginName values
• align the bundled prompt, scaffold help text, and marketplace reference spec with the new default

Testing

Tests: targeted skill validation, Python compile checks, personal-default scaffold smoke, repo-override scaffold smoke, and whitespace checks.

[xl-openai]

we should already support codex://plugins/plugin_name@workspace_name