Fix webhook active check and improve admin plugin edit screen

[simonhamp]

Summary

• Webhook endpoint: Only reject plugins where is_active is false instead of checking approval status — allows all active plugins to receive webhook data regardless of their review status
• Admin plugin edit: Link composer package name to Packagist for free plugins, hide repo URL for paid third-party plugins, link license to license page for paid plugins (GitHub for free), and add a "Go to User" action on the submitter field
• Plugin model: Add isActive() method and inactive() factory state

Test plan

• Webhook rejects inactive plugins with 403
• Webhook allows unapproved but active plugins
• Ping events still work for all plugins
• Free plugin name links to Packagist
• Paid plugin name shows plain text
• Paid third-party plugin hides repository URL
• Paid official plugin still shows repository URL
• Paid plugin license links to license page
• Free plugin license links to GitHub LICENSE
• Go to User action visible on edit plugin page

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