Windows: shippable cross-compiled .zip + console fix + release CI

The tree already links a working x86_64-pc-windows-gnu exe; turn that into
a shipped artifact:

- scripts/package.sh gains a `win` target (and `all` picks it up when the
  mingw toolchain is present) that cross-compiles and zips the exe +
  LICENSE + a README listing the yt-dlp/ffmpeg/mpv PATH deps.
- Forgejo release workflow installs mingw-w64 + zip + the rust target, so
  a tag push produces yt-offline-<ver>-x86_64-windows.zip from the same
  Linux container — no Windows runner needed.
- main.rs: attach_windows_console() (cfg(windows), windows-sys
  AttachConsole) reattaches a release build to the launching terminal so
  --web/CLI output is visible, while a double-click stays windowless
  (release sets windows_subsystem = "windows").
- ROADMAP 3.1 updated: Windows ships; macOS deferred (needs a Mac runner).

Native Linux build + 128 unit / 11 integration tests still green.

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

Cargo.lock

@@ -5432,6 +5432,7 @@ dependencies = [
  "tokio-util",
  "toml",
  "tower-http 0.5.2",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]