Add window rules for gaming/RuneLite, fix Java Wayland blank window

environment.d/wayland.conf

@@ -1 +1,2 @@
 ELECTRON_OZONE_PLATFORM_HINT=auto
+_JAVA_AWT_WM_NONREPARENTING=1

niri/config.kdl

@@ -75,3 +75,36 @@ binds {
     XF86MonBrightnessUp   allow-when-locked=true { spawn "brightnessctl" "set" "+10%"; }
     XF86MonBrightnessDown allow-when-locked=true { spawn "brightnessctl" "set" "10%-"; }
 }
+
+// ── Window Rules ─────────────────────────────────────────────────────────────
+
+// Fullscreen games: no border, open fullscreen, enable VRR
+window-rule {
+    match app-id="steam_app_"
+    open-fullscreen true
+    border {
+        off
+    }
+    focus-ring {
+        off
+    }
+    variable-refresh-rate true
+}
+
+// Generic fullscreen request (any app asking to go fullscreen)
+window-rule {
+    match is-focused=true
+    variable-refresh-rate true
+}
+
+// RuneLite (Java app-id pattern - verify with: niri msg pick-window)
+window-rule {
+    match app-id="^(net-runelite-client-RuneLite|runelite|RuneLite)$"
+    open-maximized true
+    border {
+        off
+    }
+    focus-ring {
+        off
+    }
+}