Add OpenAI Ads conversions plugin

[tej-oai]

Summary

• add the OpenAI Ads Conversions public Codex plugin
• package the conversions setup skill, public Ads documentation references, and local verification helpers
• add the plugin to both public marketplace files so standard and API-key-login Codex users can install it
• include portable usage guidance for users who cannot use Codex plugins and need to load the skill instructions in another tool

Public readiness

• removed internal dogfooding/internal marketplace install text from the README
• scanned for internal-only terms, test Pixel IDs, dogfooding notes, and stale local setup references
• kept deployment review guidance for privacy, security, consent, data handling, and CAPI secret handling

Validation

• /Users/tej/.virtualenvs/openai/bin/python /Users/tej/.codex/skills/.system/plugin-creator/scripts/validate_plugin.py plugins/openai-ads-conversions
• /Users/tej/.virtualenvs/openai/bin/python /Users/tej/.codex/skills/.system/skill-creator/scripts/quick_validate.py plugins/openai-ads-conversions/skills/openai-ads-conversions-setup
• python3 plugins/openai-ads-conversions/skills/openai-ads-conversions-setup/scripts/verify_capi_secret_not_exposed.py plugins/openai-ads-conversions --fail-on high
• python3 -m json.tool on both marketplace files and plugin.json
• node plugins/plugin-eval/scripts/plugin-eval.js analyze plugins/openai-ads-conversions --format markdown

Plugin Eval reported no failures, with warnings around token budget, helper script complexity/line length, and missing tests for helper scripts. Those helper scripts are copied from the internal dogfood plugin payload and can be tightened in follow-up if reviewers want that before public release.