Per-distro packaging: .deb / .rpm / AppImage + CI (1.8)

Ships beyond the Arch PKGBUILD so non-Arch users can install without a
Rust toolchain.

## Package metadata (Cargo.toml)

- [package.metadata.deb] for cargo-deb: declares the runtime subprocess
  deps (yt-dlp, ffmpeg, mpv, xdg-utils) that auto-detection can't find,
  plus libxcb1/libc6 link deps and libnotify4 as recommended.
- [package.metadata.generate-rpm] for cargo-generate-rpm with the
  RPM-distro dep names.
- Filled in license / repository / authors / readme package fields.

## scripts/package.sh

One entry point: `scripts/package.sh [deb|rpm|appimage|all]`. Builds the
release binary once and reuses it. Installs cargo-deb / cargo-generate-rpm
on demand; downloads appimagetool to dist/tools/ on first AppImage build.
Per-format failures are isolated and summarized at the end rather than
aborting the run. Output to dist/ (gitignored).

AppImage is hand-rolled (AppDir + AppRun + root desktop/icon) and bundles
only the GUI binary's shared-lib closure — yt-dlp/ffmpeg/mpv stay host
PATH deps, same as the package declarations.

## CI

.forgejo/workflows/release.yml builds all formats on a v* tag push and
attaches them to the Codeberg release via actions/forgejo-release. Manual
workflow_dispatch builds without uploading for smoke testing. Sets
APPIMAGE_EXTRACT_AND_RUN since CI containers lack FUSE.

## docs/PACKAGING.md

Per-format build + install instructions, the Arch PKGBUILD pointer, and
an honest Windows/macOS section: both are blocked on the Linux-only tray
(ksni) + file-picker (rfd xdg-portal) deps needing per-OS abstraction.
The rest of the stack already cross-compiles.

Verified .deb (dpkg control + payload correct) and .rpm (payload correct)
build cleanly through the script on this host.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/PACKAGING.md

@@ -0,0 +1,102 @@
+# Packaging yt-offline
+
+This document covers building distributable packages. The one-liner:
+
+```sh
+scripts/package.sh all     # .deb + .rpm + .AppImage into dist/
+scripts/package.sh deb     # just the .deb
+scripts/package.sh rpm     # just the .rpm
+scripts/package.sh appimage
+```
+
+The script builds the release binary once and reuses it for every
+format. Output lands in `dist/` (gitignored).
+
+## Linux formats
+
+### .deb (Debian / Ubuntu / Mint)
+
+Built by [`cargo-deb`](https://github.com/kornelski/cargo-deb), driven by
+`[package.metadata.deb]` in `Cargo.toml`. The script installs cargo-deb
+on demand. Runtime deps declared: `yt-dlp`, `ffmpeg`, `mpv`, `xdg-utils`,
+`libxcb1`, `libc6` (and `libnotify4` recommended).
+
+```sh
+scripts/package.sh deb
+sudo apt install ./dist/yt-offline_*_amd64.deb
+```
+
+### .rpm (Fedora / RHEL / openSUSE)
+
+Built by [`cargo-generate-rpm`](https://github.com/cat-in-136/cargo-generate-rpm),
+driven by `[package.metadata.generate-rpm]`. It packages the
+already-built (and release-profile-stripped) binary.
+
+```sh
+scripts/package.sh rpm
+sudo dnf install ./dist/yt-offline-*.x86_64.rpm
+```
+
+Note: `ffmpeg` on Fedora lives in [RPM Fusion](https://rpmfusion.org/);
+the dependency is declared but the user may need that repo enabled.
+
+### AppImage (any Linux)
+
+A hand-rolled AppDir + [`appimagetool`](https://github.com/AppImage/appimagetool)
+(downloaded to `dist/tools/` on first run). The image bundles the GUI
+binary and its shared-library closure only — `yt-dlp`/`ffmpeg`/`mpv` are
+still expected on the host PATH, same as the package deps. Bundling them
+would balloon the image and tangle the licensing.
+
+```sh
+scripts/package.sh appimage
+chmod +x dist/yt-offline-*-x86_64.AppImage
+./dist/yt-offline-*-x86_64.AppImage
+```
+
+## Arch Linux
+
+Use the `PKGBUILD` in the repo root (not this script). It builds from a
+fresh git clone, so run it from a clean directory:
+
+```sh
+mkdir build && cd build
+cp /path/to/repo/PKGBUILD .
+makepkg -si
+```
+
+For repeated builds after pushing new commits, always pass `-C`
+(cleanbuild) so makepkg re-checks out the latest source instead of
+reusing a stale cached clone.
+
+## Windows — experimental
+
+Windows is **not** currently a first-class target. Two Linux-only
+dependencies block a clean `--target x86_64-pc-windows-gnu` build:
+
+- **`ksni`** (system tray) — talks to the freedesktop StatusNotifierItem
+  D-Bus spec, which doesn't exist on Windows. Needs replacing with
+  `tray-icon` behind `#[cfg(windows)]`, or stubbing `src/tray.rs` to a
+  no-op on non-Unix.
+- **`rfd` xdg-portal backend** — the file picker uses the XDG desktop
+  portal. The `rfd` crate does support a native Windows backend, but the
+  feature flags in `Cargo.toml` would need to be made target-conditional.
+
+Once those are addressed, the rest (eframe, axum, rusqlite-bundled) is
+already cross-platform — `bundled_ytdlp_path()` and friends already have
+`cfg!(windows)` branches. The path to a Windows `.exe`/`.msi` (via
+[`cargo-wix`](https://github.com/volks73/cargo-wix)) is then mechanical.
+
+Tracked as a follow-up; PRs welcome.
+
+## macOS
+
+Same shape as Windows: the tray needs a macOS backend. eframe runs fine
+on macOS otherwise. A `.app` bundle + `.dmg` would follow once the tray
+is abstracted behind a trait with per-OS implementations.
+
+## CI
+
+`.forgejo/workflows/release.yml` runs `scripts/package.sh all` on every
+pushed tag (`v*`) and attaches the resulting `.deb`/`.rpm`/`.AppImage` to
+the Codeberg release. See that file for the runner setup.