build: package haul as a macOS .app bundle

Double-clicking the bare binary in Finder opens a Terminal window alongside
the app: Finder has no better idea what to do with a Mach-O executable than
hand it to Terminal.app, and the terminal stays up as long as the process
does. macOS has no counterpart to -H=windowsgui, so the only fix is to ship
an application bundle, which Finder launches directly.

Add `make package-darwin`, which runs a pinned `fyne package --target
darwin` to produce ./haul.app. Its metadata comes from cmd/haul/FyneApp.toml
— the app ID there must stay in step with the one app.NewWithID uses, or
macOS treats the bundle and the running app as separate applications. The
icon is a placeholder; `fyne package` will not run without one.

Note that `fyne package` rewrites FyneApp.toml in place on every run, so the
file is left in that tool's canonical formatting rather than a commented
version it would only strip again.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -205,6 +205,51 @@ Unlike Linux, Windows needs no graphics development *packages* to build: OpenGL
 ships with the operating system. Getting a usable OpenGL at **run** time is a
 separate matter — see below.
 
+### Packaging on macOS
+
+`make build` produces a plain Unix executable, and that is all you need if you
+launch haul from a shell. **Double-click it in Finder, though, and macOS opens a
+Terminal window alongside the app.** That is not a bug in haul and no build flag
+fixes it — it is what Finder does with any bare executable: having no better
+idea what a Mach-O file is, it hands it to Terminal.app to run, and the terminal
+stays on screen for as long as the process does. macOS has no equivalent of
+Windows' `-H=windowsgui`.
+
+The fix is to ship an application *bundle* — a `haul.app` directory carrying an
+`Info.plist` — which Finder launches directly, with a Dock icon and no terminal:
+
+```sh
+make package-darwin     # -> ./haul.app
+```
+
+Then drag `haul.app` into `/Applications`. Run it on a Mac: it compiles with the
+host cgo toolchain, and it builds for the host architecture, so an Intel Mac
+gives you an `amd64` bundle and Apple silicon an `arm64` one.
+
+Under the hood that target runs [`fyne
+package`](https://docs.fyne.io/started/packaging), which reads its metadata from
+`cmd/haul/FyneApp.toml`, converts `cmd/haul/Icon.png` into the bundle's
+`.icns` icon, and writes the `Info.plist`. Without `make`:
+
+```sh
+go run fyne.io/tools/cmd/fyne@v1.7.2 package --target darwin --src ./cmd/haul --release
+```
+
+Note that `fyne package` **rewrites `cmd/haul/FyneApp.toml` in place**, bumping
+`Build` on every run and dropping any comments you add to it. That is by design;
+commit the bump or discard it as you prefer.
+
+The bundle is unsigned, so Gatekeeper blocks the first launch on any Mac that
+did not build it. Right-click the app and choose **Open** (once — after that it
+starts normally), or clear the quarantine flag:
+
+```sh
+xattr -dr com.apple.quarantine /Applications/haul.app
+```
+
+Signing and notarising properly needs a paid Apple Developer ID, after which
+`fyne release --target darwin --certificate <name>` handles it.
+
 ### Running over Remote Desktop (or in a VM)
 
 A build that compiles perfectly will still fail to start in an RDP session with:
@@ -269,7 +314,8 @@ Software rendering is slower than a GPU, but haul draws two tables and some text
 | `make run`        | Build, then run (needs a `DISPLAY`)                       |
 | `make run-xvfb`   | Build, then run against a virtual X display               |
 | `make dist`       | Release binary into `./dist`                              |
-| `make clean`      | Remove `bin/` and `dist/`                                 |
+| `make package-darwin` | macOS `.app` bundle into `./haul.app` (run on a Mac)   |
+| `make clean`      | Remove `bin/`, `dist/` and `haul.app/`                     |
 
 The Makefile picks up a Go toolchain at `~/.local/go/bin/go` if one is there,
 falling back to whatever `go` is on `PATH` — so it works on machines where Go
@@ -297,7 +343,9 @@ toolchain:
 | `windows/amd64` | `gcc-mingw-w64`                                     |
 | `darwin/*`      | a Mac, or [osxcross](https://github.com/tpoechtrager/osxcross) |
 
-For that reason `make dist` builds only the native binary. The practical route
+For that reason `make dist` builds only the native binary — and on macOS the
+binary alone is not the artefact you want to hand out, see [Packaging on
+macOS](#packaging-on-macos). The practical route
 to the others is [`fyne-cross`](https://github.com/fyne-io/fyne-cross), which
 does each build inside a Docker image carrying the right toolchain: