desktop: centralize Gruvbox palette and refine Waybar/Dunst readability

Introduce a shared desktop palette for WM and notifications, then apply it across Hyprland/Waybar/Hyprlock/Dunst while tuning status module visuals (battery state cues, resource thresholds, icon alignment, and Dunst font size) for a more consistent Gruvbox experience.

modules/desktop/themes/_palette.nix

@@ -0,0 +1,54 @@
+let
+  mkHex = value: "#${value}";
+  mkRgb = value: "rgb(${value})";
+
+  base = {
+    bg0Hard = "1d2021";
+    bg0 = "282828";
+    bg0Soft = "32302f";
+    bg1 = "3c3836";
+    bg2 = "504945";
+    bg3 = "665c54";
+
+    fg0 = "fbf1c7";
+    fg1 = "ebdbb2";
+    fg4 = "a89984";
+
+    red = "fb4934";
+    orange = "fe8019";
+    yellow = "fabd2f";
+    green = "b8bb26";
+    aqua = "8ec07c";
+    blue = "83a598";
+    purple = "d3869b";
+  };
+
+  hex = builtins.mapAttrs (_: mkHex) base;
+  rgb = builtins.mapAttrs (_: mkRgb) base;
+in
+{
+  inherit base hex rgb;
+
+  semantic = {
+    bg = hex.bg0;
+    bgAlt = hex.bg1;
+    bgHover = hex.bg3;
+    bgStrong = hex.bg0Hard;
+
+    fg = hex.fg1;
+    fgMuted = hex.fg4;
+
+    accent = hex.orange;
+    info = hex.blue;
+    success = hex.green;
+    warning = hex.yellow;
+    critical = hex.red;
+
+    borderActiveRgb = rgb.orange;
+    borderInactiveRgb = rgb.bg2;
+
+    lockInnerRgb = rgb.bg0Soft;
+    lockOuterRgb = rgb.orange;
+    lockTextRgb = rgb.fg1;
+  };
+}