feat(skill): ship the codeman agent skill as a Claude Code plugin from the repo's own marketplace

`.claude-plugin/marketplace.json` at the repo root makes
`/plugin marketplace add Ark0N/Codeman` work, and the one plugin it lists is
the repo itself (`source: "./"`), whose one component is `skills/codeman/`.
So `/plugin install codeman@codeman` is a third install route next to
`npx skills add` and `codeman skill install`, and the skill shows up in the
plugin directories that index Claude Code marketplaces.

Both manifests carry package.json's version: `scripts/sync-plugin-version.mjs`
rewrites them inside `version-packages`, right after `changeset version`, and
`test/plugin-manifest.test.ts` pins the equality, the skill's frontmatter name
(without it the installed skill would be named after a versioned cache dir),
and that no other plugin component (`commands/`, `agents/`, `hooks/`,
`.mcp.json`, `settings.json`) appears at the repo root, since an install would
silently ship it.

Verified with `claude plugin validate` (one expected warning: CLAUDE.md at a
plugin root is not plugin context) and a local marketplace add, install,
details, uninstall cycle against a clean checkout of this commit.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

package.json

@@ -36,7 +36,7 @@
     "check:public-assets": "node scripts/check-public-assets.mjs",
     "capture:subagents": "node scripts/capture-subagent-screenshots.mjs",
     "changeset": "changeset",
-    "version-packages": "changeset version && npm install --package-lock-only && node scripts/check-lockfile-sync.mjs",
+    "version-packages": "changeset version && node scripts/sync-plugin-version.mjs && npm install --package-lock-only && node scripts/check-lockfile-sync.mjs",
     "check:lockfile": "node scripts/check-lockfile-sync.mjs",
     "knip": "npx --yes knip@latest --config config/knip.json",
     "release": "changeset publish",