Add Claude Code marketplace manifest with proper architecture

[AndreyVMarkelov]

Summary

Adds Claude Code marketplace support with proper self-contained plugin architecture following official specifications.

Architecture

Canonical source (platform-neutral):

skills/dbxcli/          # Source of truth - usable by ChatGPT/OpenClaw/Codex

Self-contained plugin (marketplace-ready):

plugin/claude/
  .claude-plugin/plugin.json
  skills/dbxcli/        # Synced copy (committed)
  hooks/
  scripts/
  README.md

Marketplace manifest:

.claude-plugin/marketplace.json
  - Uses "source" field (not "path") per spec
  - Includes required "owner" object
  - Points to ./plugin/claude (checked-in, not dist/)

Changes

New Files

• .claude-plugin/marketplace.json - Marketplace catalog (per official spec)
• plugin/claude/skills/dbxcli/ - Self-contained skill copy
• scripts/sync-claude-skill.sh - Sync canonical skill to plugin

Updated Files

• scripts/test-plugin.sh - Validates marketplace structure and skill sync
• .github/workflows/ci.yml - Adds CI job that fails if skills are out of sync
• .gitignore - Ignore tmp/ directory

Official Spec Compliance

✅ Marketplace manifest location: .claude-plugin/marketplace.json
✅ Plugin entry uses source field (not path)
✅ Required owner object at top level
✅ Self-contained plugin (no path escaping after install)
✅ CI enforces sync between canonical and plugin copies

Installation Flow

Before (requires clone):

git clone https://github.com/dropbox/dbxcli.git
cd dbxcli
claude --plugin-dir dist/claude/dbxcli-plugin

After (zero-clone marketplace install):

/plugin marketplace add Dropbox/dbxcli
/plugin install dbxcli@dbxcli

Then use: /dbxcli:dbxcli list my Dropbox files

Benefits

1. Self-contained marketplace plugin - No path escaping issues after install
2. Canonical source remains platform-neutral - ChatGPT/OpenClaw can continue using skills/dbxcli/
3. Claude packaging not source of truth - dist/ stays as build artifact
4. No committing generated code - dist/ remains in .gitignore
5. CI-enforced synchronization - Build fails if copies diverge

Validation

All validation tests pass (30/30):

./scripts/test-plugin.sh
=== Results: 30 passed, 0 failed ===

CI checks:

• ✅ Marketplace.json is valid JSON with required fields
• ✅ Plugin skill matches canonical source
• ✅ All plugin structure validations pass