Fix: Stop the display link retraining and blanking

This panel's DP link is marginal. 4500x3000@60 at 10bpc is around 24 Gbps,
right at the edge of DP 1.4 HBR3 and reliant on DSC, so every modeset
retrains the link and blanks the screen. 8bpc keeps headroom.

Steam games are the other trigger. Everything Hyprland does only for a real
fullscreen window (direct scanout, VRR, tearing, auto HDR) forces that
retrain, so steam_app windows get fullscreen_state "1 2": maximized
internally while the game believes it is fullscreen, which is what
borderless windowed looks like from the game's side.

Recorded alongside the related Panama settings already at 0,
directScanoutPolicy and vrrPolicy.

config/dot/hypr/rules.lua

@@ -125,6 +125,16 @@ hl.window_rule({
     no_dim    = true,
 })
 
+-- Steam games never get true fullscreen. Everything Hyprland does only for a
+-- real fullscreen window (direct scanout, VRR, tearing, auto HDR) makes this
+-- panel's marginal DP link retrain and blank (2026-09-13). "1 2" keeps the
+-- window maximized internally while the game believes it is fullscreen, which
+-- is what borderless windowed looks like from the game's side.
+hl.window_rule({
+    match = { class = "^steam_app_\\d+$" },
+    fullscreen_state = "1 2",
+})
+
 -- Steam itself is a normal window, but its transient popups are a mess.
 hl.window_rule({
     match = { class = "^steam$", title = "^(Friends List|Steam Settings|Special Offer.*)$" },