feat(nunc): add nunc floating clock overlay package and service

- Add packages/nunc derivation built from Gitea with swiftPackages
- Add home module reichard.services.nunc with configurable settings
  and launchd agent for macOS
- Enable nunc service on mac-va-mbp-work
- Tweak mac-va-mbp-work defaults: hide menu bar, disable auto
  brightness, hide Finder desktop icons

homes/aarch64-darwin/evanreichard@mac-va-mbp-work/default.nix

@@ -40,6 +40,10 @@ in
       };
     };
 
+    services = {
+      nunc = enabled;
+    };
+
     security = {
       sops = enabled;
     };

modules/home/services/nunc/default.nix

@@ -0,0 +1,109 @@
+{ config
+, lib
+, pkgs
+, namespace
+, ...
+}:
+let
+  cfg = config.${namespace}.services.nunc;
+in
+{
+  options.${namespace}.services.nunc = {
+    enable = lib.mkEnableOption "nunc floating clock overlay";
+
+    settings = lib.mkOption {
+      type = lib.types.submodule {
+        options = {
+          fontSize = lib.mkOption {
+            type = lib.types.number;
+            default = 12;
+            description = "Font size for the clock display.";
+          };
+
+          verticalPadding = lib.mkOption {
+            type = lib.types.number;
+            default = 9;
+            description = "Vertical padding around the clock text.";
+          };
+
+          horizontalPadding = lib.mkOption {
+            type = lib.types.number;
+            default = 20;
+            description = "Horizontal padding around the clock text.";
+          };
+
+          position = lib.mkOption {
+            type = lib.types.enum [
+              "top_left"
+              "top_center"
+              "top_right"
+              "bottom_left"
+              "bottom_center"
+              "bottom_right"
+            ];
+            default = "top_right";
+            description = "Position of the clock overlay on screen.";
+          };
+
+          offsetX = lib.mkOption {
+            type = lib.types.number;
+            default = -12;
+            description = "Horizontal offset from the base position.";
+          };
+
+          offsetY = lib.mkOption {
+            type = lib.types.number;
+            default = 4;
+            description = "Vertical offset from the base position.";
+          };
+
+          dateFormat = lib.mkOption {
+            type = lib.types.str;
+            default = "EEE MMM d HH:mm:ss";
+            description = "Date format string (NSDateFormatter / Unicode TR35 format).";
+          };
+        };
+      };
+      default = { };
+      description = "Nunc configuration. Written to ~/.config/nunc/config.json.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = pkgs.stdenv.isDarwin;
+        message = "reichard.services.nunc is only supported on macOS (Darwin).";
+      }
+    ];
+
+    home.packages = [ pkgs.reichard.nunc ];
+
+    home.file.".config/nunc/config.json" = {
+      text = builtins.toJSON {
+        inherit (cfg.settings)
+          fontSize
+          verticalPadding
+          horizontalPadding
+          position
+          offsetX
+          offsetY
+          dateFormat
+          ;
+      };
+    };
+
+    launchd.agents.nunc = {
+      enable = true;
+      config = {
+        Label = "io.reichard.nunc";
+        Program = "${pkgs.reichard.nunc}/bin/nunc";
+        RunAtLoad = true;
+        KeepAlive = true;
+        ProcessType = "Interactive";
+        StandardOutPath = "${config.home.homeDirectory}/Library/Logs/nunc/nunc.out.log";
+        StandardErrorPath = "${config.home.homeDirectory}/Library/Logs/nunc/nunc.err.log";
+      };
+    };
+  };
+}

packages/nunc/default.nix

@@ -0,0 +1,48 @@
+{ lib
+, swiftPackages
+, fetchgit
+,
+}:
+
+swiftPackages.stdenv.mkDerivation rec {
+  pname = "nunc";
+  version = "unstable-2026-04-15";
+
+  src = fetchgit {
+    url = "https://gitea.va.reichard.io/evan/Nunc.git";
+    rev = "95d95840aa0bc7b595293c6c5c9f53d120a90cca";
+    hash = "sha256-UXBKcEuNnVO7WzuvmVqXMiJH7uvjLkcWiqBO0BhynsU=";
+  };
+
+  nativeBuildInputs = [
+    swiftPackages.swift
+    swiftPackages.swiftpm
+  ];
+
+  buildInputs = [
+    swiftPackages.Foundation
+    swiftPackages.XCTest
+  ];
+
+  buildPhase = ''
+    runHook preBuild
+    swift build -c release
+    runHook postBuild
+  '';
+
+  installPhase = ''
+    runHook preInstall
+    mkdir -p $out/bin
+    cp .build/release/Nunc $out/bin/nunc
+    runHook postInstall
+  '';
+
+  meta = {
+    description = "Minimal floating clock overlay for macOS";
+    homepage = "https://gitea.va.reichard.io/evan/Nunc";
+    license = lib.licenses.mit;
+    maintainers = with lib.maintainers; [ evanreichard ];
+    mainProgram = "nunc";
+    platforms = lib.platforms.darwin;
+  };
+}

systems/aarch64-darwin/mac-va-mbp-work/default.nix

@@ -28,12 +28,20 @@
       KeyRepeat = 2;
       NSWindowShouldDragOnGesture = true;
       AppleICUForce24HourTime = true;
+      _HIHideMenuBar = true;
     };
     WindowManager = {
       HideDesktop = true;
     };
+    finder = {
+      CreateDesktop = false;
+    };
   };
 
+  system.activationScripts.postActivation.text = ''
+    sudo defaults write /Library/Preferences/com.apple.iokit.AmbientLightSensor "Automatic Display Enabled" -bool false
+  '';
+
   security.pam.services.sudo_local.touchIdAuth = true;
 
   reichard = { };