web: convert changelogs from old format

https://gist.github.com/dumbmoron/3fc6c0c747d791928aba939976fd9304

web/changelogs/5.3.md

@@ -0,0 +1,20 @@
+---
+title: "better looks, better feel"
+banner:
+    file: "cattired.webp"
+    alt: "a cat laying on a sofa face down, wiggling its tail"
+---
+this update isn't as big as previous ones, but it still greatly enhances the cobalt experience.
+
+here's what's up:
+- new mode switcher! elegant and 100% clear. should no longer cause any confusion. let me know if you like it better this way :D
+- wide paste button on mobile is back, but now it's even closer to your finger.
+- removed the weird grey chin on changelog banners.
+- removed left-handed layout toggle since it is no longer needed.
+- fixed input area display in chromium 112+.
+- centered the main action box.
+- cleaned up css of main action box to get rid of tricks and ensure correct display on all devices.
+- fixed a bug that'd cause notifications dots to disappear when an unrelated checkbox was checked.
+
+hopefully from now on i'll focus on adding support for more services.
+thank you for using cobalt. stay cool :)