feat(packaging): add a thin AppImage build

build-appimage.sh produces pixelpass-<version>-x86_64.AppImage via
linuxdeploy. PixelPass links almost nothing (only libpipewire, which is
excludelisted) and shells out to gst-launch-1.0/pactl/a player on the host
PATH, while its GUI graphics libs are dlopen'd and also excludelisted — so
the AppImage bundles just the binary, AppRun, desktop entry, and icon
(~13 MB, zero bundled libs). The no-sandbox model lets the bundled binary
spawn the host's tools, which is why AppImage fits this orchestrator better
than Flatpak.

AppRun opens --gui when launched with no args and no controlling terminal
(file manager / .desktop), and passes through otherwise so the CLI,
interactive menu, and viewer all work. README documents the host-deps
contract + the glibc-baseline and VAAPI caveats.

Verified: builds to 13 MB; --version/--help work; the GUI launches cleanly
on a live Wayland session via both --gui and the no-tty AppRun path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/appimage/.gitignore

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+.tools/
+AppDir/
+*.AppImage

packaging/appimage/AppRun

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+#!/bin/sh
+# AppRun for the PixelPass AppImage.
+#
+# PixelPass is an orchestrator: it shells out to gst-launch-1.0, pactl, and a
+# player (mpv/vlc) found on the host PATH. We prepend our own usr/bin so any
+# bundled helpers win, but the host's tools remain reachable — that's why this
+# app suits AppImage (no sandbox) better than a Flatpak.
+HERE="$(dirname "$(readlink -f "$0")")"
+export PATH="$HERE/usr/bin:$PATH"
+
+BIN="$HERE/usr/bin/pixelpass"
+
+# With no arguments and no controlling terminal — i.e. launched from a file
+# manager or the .desktop entry — open the GUI. From a terminal, or with any
+# argument (a ticket, --host, --gui, --repair, …), pass through so the CLI and
+# the interactive menu both work.
+if [ "$#" -eq 0 ] && [ ! -t 0 ]; then
+  exec "$BIN" --gui
+fi
+exec "$BIN" "$@"

packaging/appimage/README.md

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+# PixelPass AppImage
+
+A "thin" AppImage: the gui-enabled `pixelpass` binary, a launcher (`AppRun`),
+and the desktop entry + icon. Run `./build-appimage.sh` to produce
+`pixelpass-<version>-x86_64.AppImage`.
+
+## Why thin
+
+`pixelpass` is an orchestrator — it links almost nothing (only `libpipewire`,
+which is excludelisted because it must match the host daemon) and instead
+**shells out** to `gst-launch-1.0`, `pactl`, and a player (`mpv`/`vlc`) found on
+the host `PATH`. The GUI's graphics libraries (`libGL`, `libwayland-*`,
+`libxkbcommon`, X11) are dlopen'd at runtime and are likewise on the AppImage
+excludelist — every desktop already has a matching set. So there is nothing
+useful to bundle, and bundling the graphics stack would only risk driver
+mismatches. The AppImage therefore carries just the binary.
+
+This also explains why PixelPass suits AppImage better than Flatpak: the
+no-sandbox model lets the bundled binary freely spawn the host's `gst-launch`,
+`pactl`, and player, which a Flatpak sandbox would block.
+
+## Host requirements
+
+The AppImage runs on any reasonably current glibc-based distro that has:
+
+- **GStreamer + plugins** — `gst-launch-1.0`/`gst-inspect-1.0` plus base,
+  good/bad/ugly, libav, and the PipeWire plugin (the binary tells you the exact
+  package names for your distro if something is missing).
+- **PipeWire** (with the PulseAudio shim, for `pactl`).
+- **A player** — `mpv` (preferred) or `vlc` — for the viewer side.
+- For X11 single-window capture: `xwininfo`.
+
+These are the same dependencies the Arch package lists; the AppImage just spares
+you the Rust toolchain.
+
+## Caveats
+
+- **Built on a bleeding-edge glibc** (CachyOS), so the AppImage requires a host
+  glibc at least that new. For broad compatibility, rebuild on an older base.
+- **Hardware encode (VAAPI `vah264enc`)** uses the host GPU driver; it can't be
+  bundled. The software path (`--no-hwencode`, x264) always works.

packaging/appimage/build-appimage.sh

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+#!/usr/bin/env bash
+# Build a "thin" PixelPass AppImage: the gui-enabled release binary plus only
+# its non-excludelisted shared libraries. The graphics stack (libGL, wayland,
+# xkbcommon, X11) is intentionally left to the host — those libs are on the
+# AppImage excludelist because they must match the host driver — and the
+# runtime tools PixelPass shells out to (gst-launch-1.0, pactl, mpv/vlc) are
+# expected on the host PATH, the same contract the Arch package documents.
+#
+# Usage: packaging/appimage/build-appimage.sh
+# Output: packaging/appimage/pixelpass-x86_64.AppImage
+set -euo pipefail
+
+here="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+repo="$(cd "$here/../.." && pwd)"
+tools="$here/.tools"
+appdir="$here/AppDir"
+mkdir -p "$tools"
+
+# linuxdeploy is itself an AppImage; run it without FUSE so this works on hosts
+# (and CI) that lack libfuse2.
+export APPIMAGE_EXTRACT_AND_RUN=1
+# Embed the version from Cargo.toml into the AppImage filename metadata.
+VERSION="$(grep -m1 '^version' "$repo/Cargo.toml" | sed -E 's/.*"(.*)".*/\1/')"
+export VERSION
+
+echo ">> building release binary (--features gui)"
+( cd "$repo" && cargo build --release --features gui )
+bin="$repo/target/release/pixelpass"
+
+echo ">> fetching linuxdeploy"
+ld="$tools/linuxdeploy-x86_64.AppImage"
+if [ ! -x "$ld" ]; then
+  curl -fL --retry 3 -o "$ld" \
+    "https://github.com/linuxdeploy/linuxdeploy/releases/download/continuous/linuxdeploy-x86_64.AppImage"
+  chmod +x "$ld"
+fi
+
+echo ">> assembling AppDir"
+rm -rf "$appdir"
+mkdir -p "$appdir/usr/bin"
+install -m755 "$bin" "$appdir/usr/bin/pixelpass"
+
+echo ">> running linuxdeploy (bundles libs, builds the AppImage)"
+# -e: analyse this binary for libraries to bundle (only libpipewire et al. that
+#     aren't excludelisted will be copied; glibc + graphics libs are skipped).
+# -d/-i: desktop entry + icon for desktop integration.
+# --custom-apprun: our launcher that opens --gui from a file manager.
+( cd "$here" && OUTPUT="pixelpass-${VERSION}-x86_64.AppImage" "$ld" \
+    --appdir "$appdir" \
+    -e "$bin" \
+    -d "$repo/assets/pixelpass.desktop" \
+    -i "$repo/assets/pixelpass-256.png" \
+    --icon-filename pixelpass \
+    --custom-apprun "$here/AppRun" \
+    --output appimage )
+
+echo ">> done: $here/pixelpass-${VERSION}-x86_64.AppImage"