feat(plasma): integrate plasma-manager with custom Breeze decoration and shortcuts

Add the plasma-manager flake input and wire it into home-manager,
along with a custom breeze-enhanced KWin decoration package, KDE
config (fonts, cursor theme, window rules), and .desktop entries
for OBS/volctl/Warudo shortcut scripts.

pkgs/breeze-enhanced.nix

@@ -0,0 +1,43 @@
+{
+  lib,
+  stdenv,
+  fetchFromGitHub,
+  cmake,
+  kdePackages,
+}:
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "breeze-enhanced";
+  version = "6.5.0";
+
+  src = fetchFromGitHub {
+    owner = "tsujan";
+    repo = "BreezeEnhanced";
+    rev = "bf9ea179b06c8e398f69f47d83cae81110ef0cc8"; # tag V6.5
+    hash = "sha256-yfN2SKJcGhPe4/7nvbRgLyux+b9rIQlm4lJINpV20Ys=";
+  };
+
+  nativeBuildInputs = [
+    cmake
+    kdePackages.extra-cmake-modules
+    kdePackages.wrapQtAppsHook
+  ];
+
+  buildInputs = with kdePackages; [
+    qtbase
+    kdecoration
+    kguiaddons
+    kwindowsystem
+    ki18n
+    kcmutils
+  ];
+
+  meta = {
+    description = "Enhanced version of the Breeze window decoration for KWin, pairs well with Kvantum themes";
+    homepage = "https://github.com/tsujan/BreezeEnhanced";
+    changelog = "https://github.com/tsujan/BreezeEnhanced/releases/tag/V${finalAttrs.version}";
+    license = lib.licenses.gpl3Only;
+    platforms = lib.platforms.linux;
+    maintainers = [ ];
+  };
+})