ci: stop syncing CLI skills to the Claude Code plugin

[erikengervall]

Why

The Firecrawl Claude Code plugin is moving to a separately released package built on Firecrawl's hosted MCP server. sync-plugin.yml replaces the plugin's whole skill tree and manifests on every skills/** change and merges that PR immediately, so while it exists it would overwrite the new package.

Summary

• Delete .github/workflows/sync-plugin.yml.
• Delete .claude-plugin/ (plugin.json, marketplace.json). The workflow was its only consumer, so after this it would ship nowhere.
• Add one README line for contributors: the Claude Code plugin is released separately and doesn't include the CLI skills.

Unchanged: sync-skills.yml (Cursor plugin), sync-catalog.yml (skills catalog), and skills/ itself. CLI users who want these skills in Claude Code keep npx skills add firecrawl/cli or the firecrawl@firecrawl-skills catalog plugin.

This revives #309 with the now-dead .claude-plugin/ manifests removed as well.

Merge order

1. This PR first.
2. Then the paired plugin package PR (firecrawl/firecrawl-plugins#9, private).
3. Then the plugin release.

Before the release, make sure no sync-plugin.yml run is queued and no open sync PR on the plugin repository can restore the old files.

Test plan

• grep across the repo (scripts, tests, docs, package.json, .npmignore, other workflows): nothing else references .claude-plugin or sync-plugin.yml.
• npx skills add ./ --list on this branch still discovers every skill in skills/, so removing the manifests doesn't affect npx skills add firecrawl/cli.
• git diff --check is clean.

---

Summary by cubic

Stops syncing CLI skills to the Firecrawl Claude Code plugin, which is now released as a separate package built on Firecrawl's hosted MCP server.

• Removes the .github/workflows/sync-plugin.yml workflow that copied skills/** and the .claude-plugin/ manifests into firecrawl/firecrawl-claude-plugin and auto-merged the resulting PR.
• Removes .claude-plugin/plugin.json and .claude-plugin/marketplace.json; the workflow was their only consumer and nothing else in the repo references them.
• Adds a contributor note that the Claude Code plugin no longer includes these CLI skills. The Cursor plugin (sync-skills.yml), skills catalog (sync-catalog.yml), and skills/ are unchanged, so npx skills add firecrawl/cli still works.

Merge this PR before the plugin package release; a queued or in-flight sync could otherwise overwrite the new package.

^{Written for commit e044ce7. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Shadow auto-approve: would require human review. Stops syncing CLI skills and manifests to the Claude Code plugin by deleting sync-plugin.yml and .claude-plugin, and adds a README note. Needs human sign-off to confirm the separately released plugin package is actually ready before disabling the existing sync.

View guided diff | Turn on auto-fix | Re-trigger cubic</sub>