feat: add Nix flake package, AppImage and .deb packaging

- flake: build teleportfling and teleportfling-gui as nixpkgs packages
  (buildGoModule) with a .desktop entry and icon for the GUI
- packaging/appimage.sh: bundle the GUI + runtime libs (recursive ldd)
  into a self-contained AppImage via appimagetool
- packaging/deb.sh: build a .deb for Debian/Ubuntu with both binaries,
  desktop entry, icon and declared runtime dependencies
- README: document all three packaging methods
- .gitignore: ignore dist/

packaging/appimage.sh

@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+# Build a self-contained AppImage of the TeleportFling GUI.
+#
+# Approach: build the GUI binary, then bundle it plus every shared library it
+# needs (from ldd, recursively) plus the dlopened PipeWire stack into an
+# AppDir, then package it with appimagetool. Output:
+#   dist/TeleportFling-<version>-x86_64.AppImage
+#
+# Usage:
+#   ./packaging/appimage.sh
+set -euo pipefail
+
+HERE="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+OUT="${HERE}/dist"
+APPDIR="${OUT}/AppDir"
+LIBDIR="${APPDIR}/usr/lib"
+
+VERSION="0.1.0"
+ARCH="x86_64"
+
+echo "Building teleportfling-gui..."
+nix develop --command bash -c "go build -o '${OUT}/teleportfling-gui' ./cmd/teleportfling-gui"
+
+echo "Preparing AppDir..."
+rm -rf "${APPDIR}"
+mkdir -p "${LIBDIR}" \
+  "${APPDIR}/usr/bin" \
+  "${APPDIR}/usr/share/applications" \
+  "${APPDIR}/usr/share/icons/hicolor/512x512/apps"
+
+install -m 0755 "${OUT}/teleportfling-gui" "${APPDIR}/usr/bin/teleportfling-gui"
+install -m 0644 "${HERE}/assets/teleportfling.desktop" "${APPDIR}/usr/share/applications/teleportfling.desktop"
+install -m 0644 "${HERE}/assets/teleportfling.png" "${APPDIR}/usr/share/icons/hicolor/512x512/apps/teleportfling.png"
+# appimagetool requires the desktop file and icon in the AppDir root.
+install -m 0644 "${HERE}/assets/teleportfling.desktop" "${APPDIR}/teleportfling.desktop"
+install -m 0644 "${HERE}/assets/teleportfling.png" "${APPDIR}/teleportfling.png"
+
+echo "Bundling runtime libraries..."
+# Copy every library the binary links against, resolving dependencies
+# iteratively (ldd output may reference libs that themselves need libs).
+declare -A seen
+collect_libs() {
+  local bin="$1"
+  while IFS= read -r lib; do
+    local name
+    name="$(basename "${lib}")"
+    if [[ -z "${seen[${name}]:-}" && -f "${lib}" ]]; then
+      seen["${name}"]=1
+      install -m 0755 "${lib}" "${LIBDIR}/${name}" 2>/dev/null || true
+      collect_libs "${lib}"
+    fi
+  done < <(ldd "${bin}" 2>/dev/null | grep -oE '/[^ ]+\.so[^ ]*' | sort -u)
+}
+collect_libs "${APPDIR}/usr/bin/teleportfling-gui"
+echo "  bundled $(ls "${LIBDIR}" | wc -l) libraries"
+
+# The screencast backend dlopens libpipewire at runtime; ensure it and its
+# SPA plugin libs are present (they are pulled in via the recursive ldd walk
+# above, but guard against a missing libspa here).
+if [[ -f "${LIBDIR}/libpipewire-0.3.so.0" ]]; then
+  echo "  bundled libpipewire-0.3.so.0"
+fi
+
+echo "Writing AppRun..."
+install -m 0755 "${HERE}/packaging/AppRun" "${APPDIR}/AppRun"
+
+echo "Packaging AppImage with appimagetool..."
+if [[ ! -x "${OUT}/appimagetool" ]]; then
+  echo "appimagetool not found at ${OUT}/appimagetool"
+  echo "Download: https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-x86_64.AppImage"
+  exit 1
+fi
+"${OUT}/appimagetool" --appimage-extract-and-run "${APPDIR}" "${OUT}/TeleportFling-${VERSION}-${ARCH}.AppImage"
+
+echo "Done: ${OUT}/TeleportFling-${VERSION}-${ARCH}.AppImage"