feat(flatpak): Flatpak manifest, AppStream metainfo, and distribution CI pipeline

[Muneerali199]

Summary

Closes #206

This PR is a GSoC 2026 proposal reference artifact for the Flatpak Distribution issue. The complete, Flathub-ready implementation will be delivered during the GSoC coding period.

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Problem

Rein has no Flatpak packaging. Linux users must build from source or use the AppImage directly (no sandboxing, no auto-update, not in any store). Flatpak would give:

• Sandboxed installs on all major distros (Fedora, Ubuntu, Arch, openSUSE…)
• Distribution through Flathub (largest Linux app store)
• Automatic updates via GNOME Software / KDE Discover

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Files added

File	Purpose
flatpak/org.aossie.Rein.yml	Flatpak manifest (app-id, finish-args, modules)
flatpak/org.aossie.Rein.desktop	.desktop entry for app launchers
flatpak/org.aossie.Rein.metainfo.xml	AppStream metainfo (required by Flathub)
flatpak/rein-wrapper.sh	Sandbox-safe launcher (--no-sandbox for Electron)
flatpak/flathub.json	Flathub submission config
.github/workflows/flatpak.yml	CI: build Flatpak bundle on tag push

---

Architecture

Flatpak sandbox (org.aossie.Rein)
├── runtime: org.freedesktop.Platform 23.08
├── base:    org.electronjs.Electron2.BaseApp
│
├── finish-args
│   ├── --socket=x11 / --socket=wayland    (display)
│   ├── --share=network                    (WebSocket / WebRTC)
│   ├── --filesystem=xdg-run/pipewire-0    (screen capture)
│   ├── --talk-name=org.freedesktop.portal.ScreenCast
│   └── --device=all                       (uinput virtual input)
│
└── modules
    ├── ydotool  (virtual input backend, built from source)
    └── rein     (Electron AppImage, extracted in-sandbox)

CI pipeline (tag push → .flatpak bundle):

git tag v1.2.3
        │
        ▼ flatpak.yml
  ubuntu-latest (bilelmoussaoui/flatpak-github-actions container)
        │
        ├── npm build → electron-builder --linux AppImage
        ├── copy AppImage → flatpak/rein-placeholder.AppImage
        ├── flatpak-builder (org.aossie.Rein.yml)
        │       └── produces rein.flatpak bundle
        ├── upload-artifact (30 days)
        └── softprops/action-gh-release → attaches to GitHub Release

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Flatpak vs AppImage comparison

	AppImage	Flatpak
Sandboxed	No	Yes (seccomp + namespaces)
Auto-update	No	Yes (via GNOME Software)
In Flathub	No	Yes (after review)
Wayland native	Partial	Yes (via portal)
ydotool included	No	Yes (bundled module)
PipeWire screen capture	No	Yes (XDG portal)

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What the full GSoC implementation will add

• Submit org.aossie.Rein.yml to flathub/org.aossie.Rein repository for review
• Replace placeholder AppImage source with proper Electron Flatpak SDK build (no AppImage-in-Flatpak antipattern)
• PipeWire portal integration for screen capture (replacing X11 XShm)
• Icon set (16×16 → 256×256 PNGs) generated from SVG
• Automated Flathub PR on every upstream release tag
• Flathub beta channel for pre-release testing

---

Note: This PR is closed immediately as a proposal artifact. Full implementation during GSoC 2026.

[Muneerali199]

Closing as a GSoC 2026 proposal reference artifact. This PR demonstrates the Flatpak packaging design for Issue #206. The complete implementation — including a proper Electron Flatpak SDK build (no AppImage-in-Flatpak), PipeWire portal integration, icon set, and Flathub submission — will be delivered during the GSoC 2026 coding period.

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Reviewing files that changed from the base of the PR and between af16487 and 6f6b781.

📒 Files selected for processing (6)

• .github/workflows/flatpak.yml
• flatpak/flathub.json
• flatpak/org.aossie.Rein.desktop
• flatpak/org.aossie.Rein.metainfo.xml
• flatpak/org.aossie.Rein.yml
• flatpak/rein-wrapper.sh

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