Add slack-desktop for aarch64 on a native Electron runtime

Slack only publishes an x86_64 Linux build, so the AUR recipe produces an
aarch64 package full of x86_64 binaries that cannot start. Run Slack's
application code on the AArch64 build of the Electron release it ships
with, replace the three native addons Slack requires at boot with
JavaScript equivalents, and drop the x86_64 addons it can do without.

pkgbuilds/slack-desktop/.omarchy/package.json

@@ -0,0 +1,9 @@
+{
+  "source": "local",
+  "upstream": {
+    "watch": {
+      "json": "https://slack.com/api/desktop.latestRelease?arch=x64&variant=deb",
+      "path": "version"
+    }
+  }
+}