Rename paid plugin badge to Premium and revamp install instructions

[simonhamp]

What

• Marketplace card badge: change the premium plugin card badge from "Paid" to "Premium" (display string only — PluginType::Paid enum, styling, and all other logic are untouched).
• Plugin show page — install box: restructure the premium install instructions into a collapsible "Installation Instructions" section (collapsed by default), containing:
  • a nested "Configure Composer" collapsible (collapsed by default) with a single code block combining the repository and credentials composer config commands (masked display for logged-in users, placeholders for guests; the copy button always copies the real values);
  • a single install command block — php artisan vendor:publish --tag=nativephp-plugins-provider, composer require <package>, php artisan native:plugin:register <package>;
  • a link to the Using Plugins guide.
• New component: extract a reusable x-plugin-command Blade component for the copyable command boxes (previously the markup was duplicated several times). It uses @js() for the clipboard value, which is more robust than the prior manual string interpolation.

Why

"Premium" reads better than "Paid" for the marketplace, and the install instructions were growing repetitive and cluttered. Collapsing them keeps the plugin page focused on the README while still giving buyers a clear, copy-paste install path.

Notes

• Collapsing is purely client-side (Alpine x-show/x-collapse), so all commands/credentials remain in the server-rendered HTML — SEO and feature-test assertions are unaffected.
• The dynamic email/key in the combined config block are escaped with e() before the unescaped {!! !!} render, keeping it XSS-safe.

Tests

• PluginDirectoryTest — paid plugin card shows the "Premium" badge.
• PluginShowInstallCredentialsTest — install commands present, credentials masked, copy command carries real values, Configure Composer collapsible renders, links to the Using Plugins guide.
• PluginShowPaidGuestTest — updated to the new "Installation Instructions" title.

All targeted tests pass; vendor/bin/pint is clean.

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