chore: scaffold tap with glabels-qt formula

Formula/glabels-qt.rb

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+class GlabelsQt < Formula
+  desc "gLabels Label Designer (Qt/C++) — Seth's packaging fork"
+  homepage "https://glabels.org"
+  url "https://git.sethpc.xyz/Seth/sethLabels.git",
+      tag:      "PLACEHOLDER_FILLED_AT_FIRST_RELEASE",
+      revision: "PLACEHOLDER_FILLED_AT_FIRST_RELEASE"
+  license "GPL-3.0-only"
+  head "https://git.sethpc.xyz/Seth/sethLabels.git", branch: "main"
+
+  depends_on "cmake"   => :build
+  depends_on "ninja"   => :build
+  depends_on "pkgconf" => :build
+  depends_on "qt"
+  depends_on "zlib"
+  depends_on "qrencode" => :recommended  # optional barcode backend
+  depends_on "zint"     => :recommended  # optional barcode backend
+
+  def install
+    system "cmake", "-S", ".", "-B", "build",
+           "-G", "Ninja",
+           "-DCMAKE_BUILD_TYPE=Release",
+           *std_cmake_args
+    system "cmake", "--build", "build"
+    system "cmake", "--install", "build"
+  end
+
+  test do
+    assert_match "gLabels", shell_output("#{bin}/glabels-batch-qt --version")
+  end
+end

README.md

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+# Seth's Homebrew tap
+
+Homebrew tap publishing macOS install for [sethLabels](https://git.sethpc.xyz/Seth/sethLabels).
+
+## Install
+
+```
+brew tap seth/tap https://git.sethpc.xyz/Seth/homebrew-tap.git
+brew install seth/tap/glabels-qt
+```
+
+The explicit URL form is required because Homebrew defaults to GitHub for tap
+names. When this repo is mirrored to GitHub at the public-flip, the URL becomes
+implicit and the tap command shortens to `brew tap seth/tap`.
+
+## Formulae
+
+| Formula | Description |
+|---------|-------------|
+| `glabels-qt` | [gLabels label designer (Qt/C++)](https://git.sethpc.xyz/Seth/sethLabels) — Seth's packaging fork of glabels-qt |
+
+## How this works
+
+`brew install seth/tap/glabels-qt` clones the sethLabels git tag pinned in
+`Formula/glabels-qt.rb`, builds Qt6 + glabels-qt from source, and installs to
+`/opt/homebrew/`. First install takes ~5–10 minutes. Subsequent
+`brew upgrade glabels-qt` runs are fast (only the version-bumped formula
+re-builds).
+
+## Per-release maintenance
+
+Each sethLabels release is one commit on this repo: bump `tag:` and `revision:`
+in `Formula/glabels-qt.rb`. No other edits expected.
+
+## Spec
+
+Design rationale lives in the sethLabels repo:
+[`sethlabels-docs/specs/2026-04-29-packaging-design.md`](https://git.sethpc.xyz/Seth/sethLabels/src/branch/main/sethlabels-docs/specs/2026-04-29-packaging-design.md) §D2, §7.