Fix plugin install instructions and add marketplace.json

[tyler-james-bridges]

Summary

• Added .claude-plugin/marketplace.json (required for /plugin marketplace add to work)
• Updated README install commands from invalid claude plugin add to correct /plugin marketplace add and /plugin install slash commands
• Added author, homepage, repository, and license fields to plugin.json

Context

Compared against jarrodwatts/claude-stt and the official plugin docs to determine the correct format.

Test plan

• Run /plugin marketplace add Abstract-Foundation/abstract-skills from within Claude Code
• Run /plugin install abstract-skills
• Verify skills load (e.g. /abstract-skills:abstract-quickstart)

✳️ Generated with Claude Code

[cursor]

PR Summary

Low Risk
Low risk metadata/docs-only change; main risk is incorrect plugin manifest fields breaking discovery/installation.

Overview
Adds a new .claude-plugin/marketplace.json manifest so the plugin can be added via /plugin marketplace add.

Updates .claude-plugin/plugin.json to include richer metadata (author, homepage, repository, license).

Fixes README.md installation instructions by replacing the invalid claude plugin add command with the correct Claude Code slash commands and updating the local install command to claude --plugin-dir.

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