fix: correct hooks.json format, remove explicit hooks path, and improve install docs

[giancarloerra]

Summary

Fix the plugin hooks loading error reported by /doctor and improve Claude Code install instructions in README.

Changes

• Wrap hooks/hooks.json events under a "hooks" key as required by Claude Code's plugin loader
• Remove explicit "hooks": "./hooks/hooks.json" path from plugin.json (auto-discovered from default location)
• Add shell commands (claude plugin marketplace add / claude plugin install) alongside the in-Claude /plugin commands in both Quick Start and Configuration sections

Type of change

• Bug fix (non-breaking change that fixes an issue)
• Documentation update

Testing

• claude plugin validate . passes
• claude --plugin-dir . loads without hook errors
• /doctor shows no socraticode errors for the inline plugin

Checklist

• My code follows the existing code style and conventions
• I have updated documentation (README.md) if needed
• I have read the Contributing Guide
• I agree to the Contributor License Agreement

Related issues

Fixes hook load error: "Invalid input: expected record, received undefined"