feat(home): mkDefault behaviour settings so downstream can plain-override

Nomarchy's Hyprland/Ghostty/Waybar settings were set at normal priority,
so a downstream `home.nix` setting any value Nomarchy already set threw a
"conflicting definition values" error — overriding required lib.mkForce,
contradicting the README's "mkDefault throughout" claim.

Now: behaviour/chrome leaves (input, misc, monitor, animations, dwindle,
gesture, decoration.blur sizing, ghostty padding/decoration, waybar
settings+style) are lib.mkDefault — a plain home.nix assignment wins.
Appearance values that flow from theme-state.json (gaps, colors,
rounding, opacity, fonts) stay at normal priority on purpose: change them
via nomarchy-theme-sync (their source of truth) or lib.mkForce to
hardcode. bind/exec-once lists stay normal priority so additions
concatenate rather than replace.

Verified: behaviour/ghostty plain overrides build; theme values still
conflict (steering to the CLI); default rendered config is byte-identical.

New docs/OVERRIDES.md with the appearance→CLI / behaviour→home.nix /
component→toggle model and worked examples; linked from the README.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/home/hyprland.nix

@@ -35,8 +35,13 @@ in
       "$mod" = "SUPER";
       "$terminal" = config.nomarchy.terminal;
 
-      monitor = [ ",preferred,auto,1" ];
+      # mkDefault so a downstream `monitor = [...]` replaces it with a
+      # plain assignment (the live ISO uses mkForce for the same reason).
+      monitor = lib.mkDefault [ ",preferred,auto,1" ];
 
+      # exec-once is a list at normal priority, so downstream additions
+      # CONCATENATE (your autostart runs alongside ours) rather than
+      # replace. Same for the bind* lists below.
       exec-once = [
         # nixpkgs' swww is awww (renamed fork); the binary is awww-daemon.
         "awww-daemon"
@@ -46,14 +51,19 @@ in
       ];
 
       # ── Theme-driven look ──────────────────────────────────────────
+      # These flow from theme-state.json and stay at NORMAL priority:
+      # change them with `nomarchy-theme-sync set ui.<key>` (the intended
+      # path), or lib.mkForce in home.nix to hardcode against the theme.
+      # The non-theme knobs around them are lib.mkDefault — override
+      # those with a plain home.nix assignment. See docs/OVERRIDES.md.
       general = {
         gaps_in = t.ui.gapsIn;
         gaps_out = t.ui.gapsOut;
         border_size = t.ui.borderSize;
         "col.active_border" = "${rgb c.accent} ${rgb c.accentAlt} 45deg";
         "col.inactive_border" = rgb c.overlay;
-        layout = "dwindle";
-        resize_on_border = true;
+        layout = lib.mkDefault "dwindle";
+        resize_on_border = lib.mkDefault true;
       };
 
       decoration = {
@@ -62,25 +72,26 @@ in
         inactive_opacity = t.ui.inactiveOpacity;
         blur = {
           enabled = t.ui.blur;
-          size = 8;
-          passes = 2;
-          popups = true;
+          size = lib.mkDefault 8;
+          passes = lib.mkDefault 2;
+          popups = lib.mkDefault true;
         };
         shadow = {
           enabled = t.ui.shadow;
-          range = 20;
-          render_power = 3;
+          range = lib.mkDefault 20;
+          render_power = lib.mkDefault 3;
           color = rgba c.mantle "aa";
         };
       };
 
+      # ── Behaviour (mkDefault → plain home.nix assignment overrides) ──
       animations = {
-        enabled = true;
-        bezier = [
+        enabled = lib.mkDefault true;
+        bezier = lib.mkDefault [
           "smooth, 0.25, 0.1, 0.25, 1.0"
           "snappy, 0.6, 0.0, 0.1, 1.0"
         ];
-        animation = [
+        animation = lib.mkDefault [
           "windows, 1, 4, snappy, popin 85%"
           "border, 1, 8, smooth"
           "fade, 1, 5, smooth"
@@ -88,29 +99,30 @@ in
         ];
       };
 
-      # ── Behaviour ──────────────────────────────────────────────────
       input = {
+        # kb_layout/variant come from nomarchy.keyboard.* — set that
+        # option (the installer writes it; it also drives tty/LUKS).
         kb_layout = config.nomarchy.keyboard.layout;
         kb_variant = config.nomarchy.keyboard.variant;
-        follow_mouse = 1;
-        touchpad.natural_scroll = true;
+        follow_mouse = lib.mkDefault 1;
+        touchpad.natural_scroll = lib.mkDefault true;
       };
 
       # dwindle:pseudotile was removed in Hyprland 0.55 (the `pseudo`
       # dispatcher still exists); setting it aborts config parsing.
-      dwindle.preserve_split = true;
+      dwindle.preserve_split = lib.mkDefault true;
 
       # Hyprland 0.51+ replaced gestures:workspace_swipe with the
       # gesture keyword — without this, touchpads have NO gestures.
-      gesture = [
+      gesture = lib.mkDefault [
         "3, horizontal, workspace"
         "4, pinch, fullscreen"
       ];
 
       misc = {
-        disable_hyprland_logo = true;
-        disable_splash_rendering = true;
-        force_default_wallpaper = 0;
+        disable_hyprland_logo = lib.mkDefault true;
+        disable_splash_rendering = lib.mkDefault true;
+        force_default_wallpaper = lib.mkDefault 0;
       };
 
       bind = [