docs: vendor the Microsoft Store badge as a PNG

GitHub sized the hotlinked SVG from its 161x44 intrinsic box rather than the
img height attribute, so the badge rendered short beside the other three.

rsvg-convert at exactly 4x intrinsic keeps the aspect ratio bit-identical and
the rounded corners transparent, matching the neighbouring badge assets. All
four now render 60px tall, and the README no longer hotlinks any image.

README.md

@@ -22,7 +22,7 @@ A modern client for Plex and Jellyfin on desktop, mobile, and TV. Built with Flu
 <a href='https://apps.apple.com/app/apple-store/id6754315964?pt=128238902&ct=GitHub&mt=8'><img height='60' alt='Download on the App Store' src='./assets/app-store-badge.png'/></a>
 <a href='https://play.google.com/store/apps/details?id=com.edde746.plezy&referrer=utm_source%3Dgithub%26utm_campaign%3Dreadme_badge'><img height='60' alt='Get it on Google Play' src='./assets/play-store-badge.png'/></a>
 <a href='https://www.amazon.com/gp/product/B0GK65CVS1'><img height='60' alt='Available at the Amazon App Store' src='./assets/amazon-badge.png'/></a>
-<a href='https://get.microsoft.com/installer/download/9n5r1s1t68h7?referrer=appbadge&cid=github'><img height='60' alt='Get it from Microsoft' src='https://get.microsoft.com/images/en-us%20dark.svg'/></a>
+<a href='https://get.microsoft.com/installer/download/9n5r1s1t68h7?referrer=appbadge&cid=github'><img height='60' alt='Get it from Microsoft' src='./assets/microsoft-badge.png'/></a>
 
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