feat(easyeffects): set autogain target per host

Desktop speakers on idols-ai use the EBU R128 broadcast standard (-23 dB), while the quiet built-in laptop speakers on 12kingdoms-shoukei keep -12 dB. Move the target out of the shared preset so each host sets its own value.

home/hosts/linux/12kingdoms-shoukei.nix

@@ -16,4 +16,7 @@ in
 
   xdg.configFile."niri/niri-hardware.kdl".source =
     mkSymlink "${config.home.homeDirectory}/nix-config/hosts/12kingdoms-shoukei/niri-hardware.kdl";
+
+  # The built-in laptop speakers are quiet, so boost above the -23 dB default.
+  services.easyeffects.extraPresets."loudness-normalization".output."autogain#0".target = -12.0;
 }

home/hosts/linux/idols-ai.nix

@@ -19,4 +19,7 @@ in
 
   xdg.configFile."niri/niri-hardware.kdl".source =
     mkSymlink "${config.home.homeDirectory}/nix-config/hosts/idols-ai/niri-hardware.kdl";
+
+  # The desktop speakers are already loud, so use the broadcast-standard -23 dB.
+  services.easyeffects.extraPresets."loudness-normalization".output."autogain#0".target = -23.0;
 }

home/linux/gui/base/media.nix

@@ -49,11 +49,10 @@
         ];
         "autogain#0" = {
           bypass = false;
-          # EasyEffects defaults to -23 dB (the EBU R128 broadcast standard),
-          # which is too quiet for playback. -12 dB is a common value in
-          # community presets (e.g. JackHack96's "Advanced Auto Gain") and
-          # still leaves enough headroom for the limiter below.
-          target = -12.0;
+          # target is set per host (home/hosts/linux/*.nix) because the
+          # comfortable loudness depends on the physical output device:
+          # -23 dB (EBU R128 broadcast standard) on desktop speakers,
+          # -12 dB on quiet laptop speakers. EasyEffects' own default is -23.
         };
         "limiter#0" = {
           bypass = false;