Oxide v0.5.2

Added

• In-app toasts in the bottom-right corner replace the yellow strip across the
  top of the window. Config and keymap errors show in red and stay until the
  next clean reload; other notices fade after a few seconds. Click any toast to
  dismiss it.
• The first launch after an update shows a toast; clicking it opens the
  changelog, rendered, in a new tab of the current workspace. Help → What's
  New (app::changelog) opens the same tab any time, and it's in the command
  palette.
• A failed update download is reported even on the automatic check, since the
  check itself just succeeded so the machine isn't offline.
• scripts/bump.sh <version> prepares the release commit (Cargo.toml,
  Cargo.lock, this file, RELEASING.md), and scripts/release.sh builds the
  notarized DMG and publishes the GitHub release with notes from this file.