Emit verified plugin install suggestion outcomes from core

[adaley-openai]

Summary

• Emit codex_plugin_install_suggestion_outcome after a sent plugin or connector install prompt resolves.
• Reuse the request suggestion ID and initiating turn context so request and outcome remain attributable to the same elicitation.
• Record selection and completion per tool while retaining aggregate completion for the elicitation.
• Verify remote plugin completion from the existing installed-plugin refresh result instead of connector availability; the existing Apps-tool refresh remains independent, with no new polling or retries.

Stack

• Depends on Add plugin install suggestion outcome analytics #31432, which adds the analytics contract and removes the redundant counter.
• Release after the server accepts the new analytics event.

Validation

• just test -p codex-core request_plugin_install (18 passed)