feat(homebrew): make the Mac app installable with Homebrew

.github/workflows/cask.yml

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+name: Cask
+
+on:
+  push:
+    branches: [production]
+    paths: [Casks/**, .github/workflows/cask.yml]
+  pull_request:
+    paths: [Casks/**, .github/workflows/cask.yml]
+
+jobs:
+  audit:
+    runs-on: macos-15
+    env:
+      HOMEBREW_NO_AUTO_UPDATE: 1
+    steps:
+      - uses: actions/checkout@v4
+      - run: brew update
+      - run: brew tap dev-null-sh/devnull "$GITHUB_WORKSPACE"
+      - run: brew trust dev-null-sh/devnull
+      - run: brew style --cask dev-null-sh/devnull/devnull
+      - run: brew audit --cask --strict --online dev-null-sh/devnull/devnull

Casks/devnull.rb

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+cask "devnull" do
+  version :latest
+  sha256 :no_check
+
+  url "https://dev-null.sh/downloads/DevNull.dmg"
+  name "DevNull"
+  desc "Social network for devs"
+  homepage "https://dev-null.sh/apps"
+
+  depends_on macos: :sonoma
+
+  app "DevNull.app"
+
+  zap trash: [
+    "~/Library/Caches/sh.dev-null.mac",
+    "~/Library/HTTPStorages/sh.dev-null.mac",
+    "~/Library/Preferences/sh.dev-null.mac.plist",
+    "~/Library/Saved Application State/sh.dev-null.mac.savedState",
+  ]
+end

README.md

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+# /dev/null for Mac
+
+The native Mac app for [/dev/null](https://dev-null.sh), a social network for devs. It needs macOS 14 or later.
+
+## Install
+
+Download the DMG from [dev-null.sh/apps](https://dev-null.sh/apps), or install it with [Homebrew](https://brew.sh):
+
+```sh
+brew tap dev-null-sh/devnull https://github.com/dev-null-sh/mac-os-app
+brew install --cask dev-null-sh/devnull/devnull
+```
+
+The cask always installs the latest release, and the app updates itself from then on.