Retire the Arch package, document AppImage desktop integration

The `triple-c-bin` package was never on the AUR, so installing it meant
downloading a file and running `pacman -U` — the same gesture as making an
AppImage executable, for a second artifact to keep building. And being
`workflow_dispatch`-only it reached 1 release in 28 (only v0.4.16 has a
`.pkg.tar.zst`), while HOW-TO-USE.md told Arch and CachyOS users to download
it from every release. A distribution channel that is absent 27 times out of
28 is worse than not promising one.

`packaging/arch/` and `.gitea/workflows/publish-arch-package.yml` are
preserved whole on `hold/arch-packaging`, the same way the disk panel and
drag-out work were held rather than deleted. What would make an Arch package
worth having is an AUR account and its SSH key as a repo secret — both
one-time manual steps that never happened; the workflow's own header already
said as much about its AUR push step.

This also closes the gap that prompted the review: nothing validated the
PKGBUILD until someone manually dispatched the workflow, making it the only
packaging path with no CI coverage. Removing it removes the untested surface
rather than adding a job to test something nobody installs.

In its place, `scripts/install-appimage.sh` does what a package manager's
install hooks would. An AppImage carries a `.desktop` entry and icons inside
itself, but nothing on the host reads them, so it never appears in the app
launcher. The script extracts the bundled icons into the user's icon theme
and writes a launcher entry — no sudo, nothing outside `~/.local/share`, and
the AppImage itself is never copied or moved.

Two details it gets right on purpose:

  * The `Exec` line is rewritten, not copied. The bundled entry says
    `Exec=triple-c`, which resolves only inside the running AppImage's own
    mount — a verbatim copy gives a launcher entry that starts nothing.
  * Extraction uses `--appimage-extract`, which needs no FUSE, so the script
    works on a machine where *running* the AppImage would first need
    `fuse2` installed. That requirement is now documented too: Arch and
    CachyOS do not ship FUSE 2 by default.

Verified against the real artifact — the AppImage from this repo's own
preview-3a49a67 release: 4 icon sizes install, `desktop-file-validate` passes
with no warnings, `--uninstall` leaves nothing behind, and shellcheck is
clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ApLYH6ybHwQFkMCtKuHrrV

HOW-TO-USE.md

@@ -43,12 +43,52 @@ Download the build for your platform from [GitHub Releases](https://github.com/s
 | **macOS** | `Triple-C_<version>_universal.dmg` | Open the `.dmg` and drag Triple-C to Applications. |
 | **Debian / Ubuntu** | `Triple-C_<version>_amd64.deb` | `sudo apt install ./Triple-C_<version>_amd64.deb` |
 | **Fedora / RHEL** | `Triple-C-<version>-1.x86_64.rpm` | `sudo dnf install ./Triple-C-<version>-1.x86_64.rpm` |
-| **Arch / CachyOS** | `triple-c-bin-<version>-1-x86_64.pkg.tar.zst` | `sudo pacman -U ./triple-c-bin-<version>-1-x86_64.pkg.tar.zst` |
-| **Other Linux** | `Triple-C_<version>_amd64.AppImage` | `chmod +x` it, then run it directly. |
+| **Arch / CachyOS / other Linux** | `Triple-C_<version>_amd64.AppImage` | `chmod +x` it, then run it directly. See the AppImage notes below. |
 
 > **macOS note:** The app is not signed or notarized. On first launch, macOS Gatekeeper may block it — right-click the app and select "Open" to bypass, or remove the quarantine attribute: `xattr -cr /Applications/Triple-C.app`.
 
-> **Arch / CachyOS note:** This package is not on the AUR — it's a `pacman`-installable file built and attached to each GitHub release by a maintainer-triggered step (`.gitea/workflows/publish-arch-package.yml`), so it can lag behind the very latest release by a bit. See [`packaging/arch/README.md`](packaging/arch/README.md) for details, including why "-bin" and what's verified about it.
+> **AppImage note:** Two things are worth knowing. Running an AppImage needs FUSE 2, which Arch and CachyOS do not install by default — `sudo pacman -S fuse2` once, or run it with `--appimage-extract-and-run` to sidestep FUSE entirely. And an AppImage is just an executable file: nothing registers it with the desktop, so it will not appear in your app launcher on its own. Run [`scripts/install-appimage.sh`](scripts/install-appimage.sh) to add a launcher entry and icons — see [Adding an AppImage to the app launcher](#adding-an-appimage-to-the-app-launcher).
+
+> **No Arch package.** There was a `triple-c-bin` `.pkg.tar.zst` attached to some releases, built by a maintainer-triggered workflow. It was never on the AUR, so installing it meant downloading a file and running `pacman -U` — no better than the AppImage — and being manual-only it reached 1 release in 28, which made the promise of it worse than not making it. The `PKGBUILD` and its workflow are preserved on the `hold/arch-packaging` branch if an AUR package is ever worth doing properly.
+
+### Adding an AppImage to the app launcher
+
+An AppImage is a single executable file and nothing else. It carries a `.desktop`
+entry and icons *inside* itself, but nothing on your system ever reads them,
+because nothing installed it — so it will not show up in your app launcher, and
+running it from a file manager gives you a generic icon in the taskbar.
+
+Put the AppImage somewhere stable first — `~/Apps` or `~/.local/bin`, not
+`~/Downloads` — because the launcher entry points at wherever the file is:
+
+```bash
+mkdir -p ~/Apps
+mv ~/Downloads/Triple-C_*_amd64.AppImage ~/Apps/
+./scripts/install-appimage.sh ~/Apps/Triple-C_0.4.17_amd64.AppImage
+```
+
+That copies the bundled icons into `~/.local/share/icons/hicolor` and writes
+`~/.local/share/applications/triple-c.desktop` pointing at the file you named.
+No sudo, nothing outside your home directory, and the AppImage itself is never
+copied or moved. To remove the entry again:
+
+```bash
+./scripts/install-appimage.sh --uninstall
+```
+
+The script rewrites the `Exec` line rather than reusing the bundled `.desktop`
+verbatim: the bundled one says `Exec=triple-c`, which resolves only inside the
+running AppImage's own mount, so a launcher entry copied straight out of the
+bundle would appear in the menu and then fail to start anything.
+
+Two follow-ups worth knowing:
+
+- **Upgrading.** The entry names one specific file. If you replace the AppImage
+  with a newer version under a different filename, re-run the script against the
+  new one. Keeping a stable name (`~/Apps/Triple-C.AppImage`) avoids this.
+- **The icon may not appear until you log out.** That is the desktop shell's
+  icon cache, not a failed install — see
+  [App Icon Missing After Installing (Linux)](#app-icon-missing-after-installing-linux).
 
 ## Prerequisites