fix(kodi): patch stremio CEF to support HiDPI scaling via env var

The beta.13 clap parser ignores unknown --force-device-scale-factor flags
and CEF Args::new() starts empty, so CLI flags never reach the CEF subprocess.
Patch src/webview/mod.rs to read STREMIO_FORCE_DEVICE_SCALE_FACTOR and pass
it to CEF via append_switch_with_value. Remove failed GTK4/master branch
build attempt (requires GTK 4.22 not yet in nixpkgs).

roles/kodi/default.nix

@@ -22,7 +22,7 @@ in
     stremioScaleFactor = mkOption {
       type = types.nullOr types.float;
       default = null;
-      description = "Scale factor for Stremio UI via GDK_BACKEND=x11 + GDK_SCALE (e.g., 2.0 for 200% scaling). Forces XWayland mode since GTK4 ignores GDK_SCALE on native Wayland.";
+      description = "Scale factor for Stremio UI (e.g., 2.0 for 200% scaling). Sets STREMIO_FORCE_DEVICE_SCALE_FACTOR which passes --force-device-scale-factor to the CEF subprocess via a source patch.";
     };
     appLauncherServer = {
       enable = mkOption {
@@ -70,22 +70,19 @@ in
       }
       else pkgs.qt-pinned.jellyfin-media-player;
 
-    # stremio-linux-shell is a GTK4/libadwaita + WebKitGTK app (not Electron/CEF).
-    # --force-device-scale-factor is a Chromium flag that it ignores entirely.
-    # On Wayland, GTK4 reads scale from the compositor via wp_fractional_scale_v1.
-    # To force a specific scale, we use GDK_BACKEND=x11 + GDK_SCALE which works
-    # reliably under XWayland. On native Wayland, GDK_SCALE is ignored.
-    # Format floats cleanly: 2.0 -> "2", 1.5 -> "1.5"
-    stremioScaleStr = let
-      sf = cfg.stremioScaleFactor;
+    # Format float for env var: 2.0 -> "2", 1.5 -> "1.5"
+    # (Nix's toString 2.0 gives "2.000000" which is unclean)
+    formatScale = sf: let
       intPart = builtins.floor sf;
-      s = builtins.toString sf;
-      m = builtins.match "([0-9]+)\\.([0-9]*[1-9])0*" s;
-      gdkScale = builtins.toString intPart;
     in if sf == intPart then builtins.toString intPart
-       else if m != null then (builtins.elemAt m 0) + "." + (builtins.elemAt m 1)
-       else s;
+       else let s = builtins.toString sf;
+                m = builtins.match "([0-9]+)\\.([0-9]*[1-9])0*" s;
+            in if m != null then (builtins.elemAt m 0) + "." + (builtins.elemAt m 1)
+               else s;
 
+    # stremio-linux-shell is CEF-based. We patch it (via flake overlay) to read
+    # STREMIO_FORCE_DEVICE_SCALE_FACTOR and pass it to CEF as
+    # --force-device-scale-factor, which is the standard Chromium flag for HiDPI.
     stremioPkg =
       if cfg.stremioScaleFactor != null
       then pkgs.symlinkJoin {
@@ -96,15 +93,14 @@ in
           mkdir -p $out/bin
           rm -f $out/bin/stremio
           makeWrapper ${pkgs.stremio-linux-shell}/bin/stremio $out/bin/stremio \
-            --set GDK_BACKEND x11 \
-            --set GDK_SCALE ${builtins.toString (builtins.floor cfg.stremioScaleFactor)}
+            --set STREMIO_FORCE_DEVICE_SCALE_FACTOR ${formatScale cfg.stremioScaleFactor}
 
-          # Update .desktop file to force XWayland + GDK_SCALE for scaling
+          # Update .desktop file to set the env var
           mkdir -p $out/share/applications
           rm -f $out/share/applications/com.stremio.Stremio.desktop
           substitute ${pkgs.stremio-linux-shell}/share/applications/com.stremio.Stremio.desktop \
             $out/share/applications/com.stremio.Stremio.desktop \
-            --replace-fail "Exec=sh -c " "Exec=env GDK_BACKEND=x11 GDK_SCALE=${builtins.toString (builtins.floor cfg.stremioScaleFactor)} sh -c "
+            --replace-fail "Exec=sh -c " "Exec=env STREMIO_FORCE_DEVICE_SCALE_FACTOR=${formatScale cfg.stremioScaleFactor} sh -c "
         '';
       }
       else pkgs.stremio-linux-shell;
@@ -155,9 +151,34 @@ in
       };
 
       services.displayManager = mkIf cfg.autologin {
-        autoLogin.enable = true;
-        autoLogin.user = "kodi";
-        defaultSession = "plasma";
+        autoLogin = {
+          enable = true;
+          user = "kodi";
+        };
+      };
+
+      # Kodi user home manager configuration
+      home-manager.users.kodi = {
+        home.stateVersion = "24.05";
+
+        # Auto-start Kodi in fullscreen after login
+        xsession = mkIf (!cfg.wayland) {
+          windowManager.command = ''
+            ${kodiPkg}/bin/kodi --fullscreen
+          '';
+        };
+
+        # Use a simple .xsession for X11 or a wayland startup script
+        home.file = mkIf cfg.wayland {
+          ".config/autostart/kodi.desktop".text = ''
+            [Desktop Entry]
+            Type=Application
+            Name=Kodi
+            Exec=${kodiPkg}/bin/kodi --fullscreen
+            X-GNOME-Autostart-enabled=true
+            Hidden=false
+          '';
+        };
       };
     };
-}
+}