feat(desktop-environment): add plasma home module

Declarative Plasma customization matching the repo's theming system:
catppuccin color scheme/look-and-feel from the shared flavor/accent
options, wallpaper via khanelinix.theme.wallpaper, gtk cursor theme,
and a floating bottom panel with configurable pinned launchers.

Author: khaneliman

modules/home/programs/graphical/desktop-environment/plasma/default.nix

@@ -0,0 +1,103 @@
+{
+  config,
+  lib,
+  pkgs,
+
+  ...
+}:
+let
+  inherit (lib) mkIf types;
+  inherit (lib.khanelinix) mkOpt;
+
+  cfg = config.khanelinix.programs.graphical.desktop-environment.plasma;
+  catppuccinCfg = config.khanelinix.theme.catppuccin;
+  cursorCfg = config.khanelinix.theme.gtk.cursor;
+
+  capitalize = s: lib.toUpper (builtins.substring 0 1 s) + builtins.substring 1 (-1) s;
+
+  wallpaperPath = name: lib.khanelinix.theme.wallpaperPath { inherit config pkgs name; };
+in
+{
+  options.khanelinix.programs.graphical.desktop-environment.plasma = {
+    enable = lib.mkEnableOption "KDE Plasma desktop environment customization";
+
+    panel = {
+      launchers = mkOpt (types.listOf types.str) [
+        "applications:org.kde.dolphin.desktop"
+        "applications:org.kde.konsole.desktop"
+        "applications:firefox.desktop"
+        "applications:steam.desktop"
+      ] "Apps pinned to the panel task manager.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = lib.optionals catppuccinCfg.enable [
+      (pkgs.catppuccin-kde.override {
+        flavour = [ catppuccinCfg.flavor ];
+        accents = [ catppuccinCfg.accent ];
+      })
+    ];
+
+    programs.plasma = {
+      enable = true;
+
+      workspace = {
+        wallpaper = wallpaperPath config.khanelinix.theme.wallpaper.primary;
+
+        colorScheme = mkIf catppuccinCfg.enable "Catppuccin${capitalize catppuccinCfg.flavor}${capitalize catppuccinCfg.accent}";
+        lookAndFeel = mkIf catppuccinCfg.enable "Catppuccin-${capitalize catppuccinCfg.flavor}-${capitalize catppuccinCfg.accent}";
+
+        cursor = mkIf (cursorCfg.name != null) {
+          theme = cursorCfg.name;
+          inherit (cursorCfg) size;
+        };
+      };
+
+      panels = [
+        {
+          location = "bottom";
+          height = 48;
+          floating = true;
+          widgets = [
+            {
+              kickoff = {
+                icon = "nix-snowflake-white";
+              };
+            }
+            {
+              iconTasks = {
+                inherit (cfg.panel) launchers;
+              };
+            }
+            "org.kde.plasma.marginsseparator"
+            {
+              systemTray.items.shown = [
+                "org.kde.plasma.volume"
+                "org.kde.plasma.networkmanagement"
+                "org.kde.plasma.bluetooth"
+              ];
+            }
+            {
+              digitalClock = {
+                calendar.firstDayOfWeek = "sunday";
+                time.format = "12h";
+              };
+            }
+            "org.kde.plasma.showdesktop"
+          ];
+        }
+      ];
+
+      kwin = {
+        effects = {
+          desktopSwitching.animation = "slide";
+          minimization.animation = "squash";
+        };
+      };
+
+      # Double-tap Meta opens the launcher; Meta+W matches GNOME-style overview
+      shortcuts.kwin."Overview" = "Meta+W";
+    };
+  };
+}