Add iOS platform clarification to README

[Copilot]

The issue requested clarification about iOS port availability.

Added an information box in README.md below the regional warning that explicitly states Metrolist is Android-only with no iOS version available. Directs iOS users to explore alternative clients.

Changes:

• New styled info box (consistent with existing warning box design) clarifying platform support
• Removed ambiguous temporal language to avoid implying future iOS support

<div style="padding: 16px; margin: 16px 0; background-color: #E3F2FD; border-left: 6px solid #2196F3; border-radius: 4px;">
<h2 style="margin: 0;"><strong>ℹ️ iOS Support</strong></h2>
Metrolist is an <strong>Android-only</strong> application. There is no iOS version available. iOS users looking for similar functionality may want to explore alternative YouTube Music clients available on the App Store.
</div>

Original prompt

Please rewrite for iOS port

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