feat(kodi): replace stremio with stremio-linux-shell and add scale factor support

Migrate from Qt-based stremio to Rust/CEF-based stremio-linux-shell.
Add stremioScaleFactor option (uses --force-device-scale-factor) for
4K TV display scaling. Set to 2.0 on boxy and gym-box.

flake.nix

@@ -298,7 +298,7 @@
           "custom-qmd" = pkgs.custom.qmd;
 
           "qt-pinned-jellyfin-media-player" = pkgsQt.jellyfin-media-player;
-          "qt-pinned-stremio" = pkgsQt.stremio;
+          # "qt-pinned-stremio" = pkgsQt.stremio;  # Replaced by stremio-linux-shell (Rust/CEF-based)
         }
         // (
           if system == "x86_64-linux" then