Adds the Claude Code plugin manifest alongside the existing Codex one, so
the same `skills/superdesign/` tree ships to both marketplaces off one repo.
- `.claude-plugin/plugin.json` - required manifest; without it
`claude plugin validate` fails with "No manifest found in directory"
- `.claude-plugin/marketplace.json` - self-hosted marketplace listing the
repo root, so users can install today via
`/plugin marketplace add superdesigndev/superdesign-skill` +
`/plugin install superdesign@superdesign`, independent of the
community-marketplace review queue
- README / INSTALL.md document the plugin path next to `npx skills add`,
and warn against installing both copies
- SKILL.md Step 0: the ChatGPT "switch to the Work tab" copy is now scoped
to ChatGPT chat; other harnesses with no shell get a neutral message
instead of being told to find a Work tab that does not exist
- CHANGELOG.md, plus AGENTS.md release notes covering the now-two manifests
Verified: `claude plugin validate` passes with `--strict` on both manifests,
and `claude --plugin-dir <repo>` loads the skill as `superdesign:superdesign`.
SToneX