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/

todo.md

@@ -18,10 +18,18 @@ Backlog of deferred / planned work, tracked outside of milestone milestones.
       systemd unit (`contrib/teleportfling.service`) that starts the headless
       CLI with its own config at `~/.config/teleportfling/daemon.json`.
 
-## Ideas (not yet scoped)
+## Future / Ideas (not yet scoped)
 
-- Live settings changes mid-stream (`flinger.SetConfig` for FPS/quality).
-- Bitrate/bandwidth tuning beyond the balanced 1080p30 default.
-- Screen capture scaling / downsampling.
-- Packaging (Nix package / AppImage / release binaries) — deliberately
-  deferred.
+- [ ] **Live settings changes mid-stream** — `flinger.SetConfig` for FPS/quality
+      without a restart.
+- [ ] **Bitrate / bandwidth tuning** — options beyond the balanced 1080p30
+      default.
+- [ ] **Screen capture scaling / downsampling** — capture a scaled region rather
+      than the monitor's native resolution.
+- [ ] **Multi-monitor verification** — the GUI monitor picker enumerates via
+      hyprctl; confirm behaviour on a real multi-monitor setup.
+- [ ] **Non-Hyprland monitor enumeration** — portal-based fallback so the picker
+      works on GNOME/KDE etc. (currently falls back to a single indexed option).
+- [ ] **Packaging** — Nix flake package, AppImage, and `.deb` for Debian/Ubuntu
+      (in progress: flake package, AppImage and .deb scripts added under
+      packaging/; verify on a real Debian/Ubuntu machine).