docs(plugin): add auto-update enable instructions

[JasonXuDeveloper]

Summary

• Fix misleading claim that plugin updates automatically (third-party marketplaces have auto-update disabled by default)
• Add clear instructions for users to enable auto-updates
• Improve all skill descriptions with more trigger keywords

Changes

README.md

• Fixed "Click" → "Toggle" for CLI accuracy
• Added step-by-step auto-update enable instructions

Skill Descriptions

Improved trigger keywords for better activation:

Skill	Added Keywords
jaction	coroutine alternative, scheduled action, timed event, polling condition, ExecuteAsync
jobjectpool	enemy pool, effect pool, memory optimization, pool prewarm, Rent Return pattern, lock-free
messagebox	modal popup, async dialog, await user input, delete/save confirmation
editor-ui	JButton, JStack, JCard, JTextField, design tokens, dark/light theme, themed button

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR corrects misleading documentation about automatic plugin updates and adds clear instructions for users to enable auto-updates for third-party Claude Code plugins.

Changes:

• Removed incorrect claim that the plugin updates automatically by default
• Added new "Enable Auto-Updates (Recommended)" section with step-by-step instructions
• Clarified that third-party plugins require manual opt-in for auto-updates

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[github-actions]

Auto-approved: Copilot review found no issues and Unity Tests passed (or were skipped for non-code changes).

[github-actions]

Auto-approved: Copilot review found no issues and Unity Tests passed (or were skipped for non-code changes).