Remove the Qt frontend

The Qt GUI was unused: out of make-app-release since March, not built by
the gate, and its app bundle could not start (no platform plugin). Every
renderer and input change had to be made in it separately. kge is the
ImGui frontend only.

Removes QtFrontend/QtInputHandler/QtRenderer, the KTE_USE_QT option and
its #if branches (Command.cc, GUITheme.h, main.cc), the Nix qt package
and dev shell, the commented-out Qt release steps, the Qt frontend plan,
and Qt mentions in AGENTS.md, DEVELOPER_GUIDE.md, REWRITE.md and code
comments. Git history keeps the code.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

default.nix

@@ -8,13 +8,10 @@
   SDL2,
   libGL,
   xorg,
-  kdePackages,
-  qt6Packages ? kdePackages.qt6Packages,
   installShellFiles,
   copyDesktopItems,
   makeDesktopItem,
   graphical ? false,
-  graphical-qt ? false,
 }:
 let
   cmakeContent = builtins.readFile ./CMakeLists.txt;
@@ -25,7 +22,7 @@ let
   version = builtins.head (builtins.match ".*set\\(KTE_VERSION \"(.+)\"\\).*" versionLine);
 in
 stdenv.mkDerivation {
-  pname = if graphical then (if graphical-qt then "kge-qt" else "kge") else "kte";
+  pname = if graphical then "kge" else "kte";
   inherit version;
 
   src = lib.cleanSource ./.;
@@ -36,8 +33,6 @@ stdenv.mkDerivation {
     installShellFiles
   ] ++ lib.optionals graphical [
     copyDesktopItems
-  ] ++ lib.optionals graphical-qt [
-    qt6Packages.wrapQtAppsHook
   ];
 
   buildInputs = [
@@ -47,14 +42,10 @@ stdenv.mkDerivation {
     SDL2
     libGL
     xorg.libX11
-  ] ++ lib.optionals graphical-qt [
-    kdePackages.qt6ct
-    qt6Packages.qtbase
   ];
 
   cmakeFlags = [
     "-DBUILD_GUI=${if graphical then "ON" else "OFF"}"
-    "-DKTE_USE_QT=${if graphical-qt then "ON" else "OFF"}"
     "-DCMAKE_BUILD_TYPE=Debug"
     "-DKTE_STATIC_LINK=OFF"
   ];
@@ -65,7 +56,7 @@ stdenv.mkDerivation {
       desktopName = "kge";
       genericName = "Text Editor";
       comment = "kyle's graphical text editor";
-      exec = if graphical-qt then "kge-qt %F" else "kge %F";
+      exec = "kge %F";
       icon = "kge";
       terminal = false;
       categories = [ "Utility" "TextEditor" "Development" ];
@@ -91,11 +82,7 @@ stdenv.mkDerivation {
     installManPage ../docs/kte.1
 
     ${lib.optionalString graphical ''
-      ${if graphical-qt then ''
-        cp kge $out/bin/kge-qt
-      '' else ''
-        cp kge $out/bin/kge
-      ''}
+      cp kge $out/bin/kge
       installManPage ../docs/kge.1
 
       mkdir -p $out/share/icons/hicolor/256x256/apps
@@ -108,6 +95,6 @@ stdenv.mkDerivation {
   meta = {
     description = "kyle's text editor" + lib.optionalString graphical " (graphical)";
     platforms = lib.platforms.unix;
-    mainProgram = if graphical then (if graphical-qt then "kge-qt" else "kge") else "kte";
+    mainProgram = if graphical then "kge" else "kte";
   };
 }