Add Slack to Install > Service (#14434)

Slack is one of the most popular apps people install from the AUR. It now
ships from the Omarchy package repository as slack-desktop, with native
x86_64 and aarch64 builds. Install it the same way as Bitwarden: one menu
entry that installs the package and then launches Slack. The commercial
apps page of the manual gets a matching section.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

manual/24-commercial-apps-services.md

@@ -18,6 +18,10 @@ You start 1Password with `Super + Shift + /`. If it isn't installed yet, that ho
 
 You start Spotify using `Super + Shift + M`. Like 1Password, the hotkey kicks off the installation first if Spotify isn't installed yet (or use _Install > Service > Spotify_ from the Omarchy menu).
 
+## Slack
+
+[Slack](https://slack.com/) is where a lot of teams do their chatting, both inside the company and with outside collaborators. Install it with _Install > Service > Slack_ from the Omarchy menu, and it'll open as soon as it's ready.
+
 ## Dropbox
 
 [Dropbox](https://www.dropbox.com/) is a great way to sync files between machines while keeping a backup in the cloud. To set it up, select _Install > Service > Dropbox_ from the Omarchy menu. Once it's running, hover the tray in the top right of the bar and right-click the Dropbox icon to finish the setup.