docs: present the verified cross-platform optimizer surface

[cdeust]

Summary

• position session-optimizer as cross-platform prompt refinement plus Claude-native session controls
• make the portable Codex/Gemini installation visible in the top-level product table
• align Codex marketplace naming and discovery keywords
• keep the boundary explicit: refine-gate is portable; context-guard, statusline, and automatic prompt hooks require Claude Code APIs
• ignore generated coverage artifacts in preparation for the OpenSSF coverage work

The GitHub repository description and topics were updated separately for cross-host discovery.

Validation

• pytest -q tests/test_portable_packaging.py — 3 passed
• JSON parse of the modified marketplace and plugin manifests
• git diff --check