Add AppearanceSettings to ely_domain

Introduces a small persistent appearance contract: WallpaperTheme
(Dawn/Violet/Mint/Slate), ThemeMode (System/Light/Dark), reduce_motion.
Defaults to Dawn + System + motion-on. Field accessors and setters live
on the struct so the core can mutate without exposing internals; serde
support uses kebab-case so the on-disk form matches the design CSS
naming.

Tests cover defaults, mutation independence, and a JSON round-trip with
the kebab-case names. serde_json is added as a dev-dependency only —
the production crate does not depend on it.

Cargo.lock

@@ -2281,6 +2281,7 @@ version = "0.1.0"
 dependencies = [
  "semver",
  "serde",
+ "serde_json",
  "thiserror 2.0.18",
  "toml 1.1.2+spec-1.1.0",
  "url",

crates/ely_domain/Cargo.toml

@@ -13,5 +13,8 @@ toml.workspace = true
 url.workspace = true
 uuid.workspace = true
 
+[dev-dependencies]
+serde_json.workspace = true
+
 [lints]
 workspace = true

crates/ely_domain/src/appearance.rs

@@ -0,0 +1,105 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Copy, Debug, Default, Deserialize, Eq, Ord, PartialEq, PartialOrd, Serialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum WallpaperTheme {
+    #[default]
+    Dawn,
+    Violet,
+    Mint,
+    Slate,
+}
+
+#[derive(Clone, Copy, Debug, Default, Deserialize, Eq, Ord, PartialEq, PartialOrd, Serialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum ThemeMode {
+    #[default]
+    System,
+    Light,
+    Dark,
+}
+
+#[derive(Clone, Copy, Debug, Deserialize, Eq, Ord, PartialEq, PartialOrd, Serialize)]
+pub struct AppearanceSettings {
+    wallpaper: WallpaperTheme,
+    theme_mode: ThemeMode,
+    reduce_motion: bool,
+}
+
+impl Default for AppearanceSettings {
+    fn default() -> Self {
+        Self {
+            wallpaper: WallpaperTheme::default(),
+            theme_mode: ThemeMode::default(),
+            reduce_motion: false,
+        }
+    }
+}
+
+impl AppearanceSettings {
+    pub fn wallpaper(&self) -> WallpaperTheme {
+        self.wallpaper
+    }
+
+    pub fn theme_mode(&self) -> ThemeMode {
+        self.theme_mode
+    }
+
+    pub fn reduce_motion(&self) -> bool {
+        self.reduce_motion
+    }
+
+    pub fn set_wallpaper(&mut self, wallpaper: WallpaperTheme) {
+        self.wallpaper = wallpaper;
+    }
+
+    pub fn set_theme_mode(&mut self, theme_mode: ThemeMode) {
+        self.theme_mode = theme_mode;
+    }
+
+    pub fn set_reduce_motion(&mut self, reduce_motion: bool) {
+        self.reduce_motion = reduce_motion;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{AppearanceSettings, ThemeMode, WallpaperTheme};
+
+    #[test]
+    fn default_settings_use_dawn_and_system_mode() {
+        let settings = AppearanceSettings::default();
+        assert_eq!(settings.wallpaper(), WallpaperTheme::Dawn);
+        assert_eq!(settings.theme_mode(), ThemeMode::System);
+        assert!(!settings.reduce_motion());
+    }
+
+    #[test]
+    fn setters_update_each_field_independently() {
+        let mut settings = AppearanceSettings::default();
+
+        settings.set_wallpaper(WallpaperTheme::Violet);
+        settings.set_theme_mode(ThemeMode::Dark);
+        settings.set_reduce_motion(true);
+
+        assert_eq!(settings.wallpaper(), WallpaperTheme::Violet);
+        assert_eq!(settings.theme_mode(), ThemeMode::Dark);
+        assert!(settings.reduce_motion());
+    }
+
+    #[test]
+    fn json_round_trip_preserves_kebab_case_variants() {
+        let settings = AppearanceSettings {
+            wallpaper: WallpaperTheme::Mint,
+            theme_mode: ThemeMode::Light,
+            reduce_motion: true,
+        };
+
+        let json = serde_json::to_string(&settings).unwrap();
+        assert!(json.contains("\"wallpaper\":\"mint\""));
+        assert!(json.contains("\"theme_mode\":\"light\""));
+
+        let restored: AppearanceSettings = serde_json::from_str(&json).unwrap();
+        assert_eq!(restored, settings);
+    }
+}

crates/ely_domain/src/lib.rs

@@ -1,3 +1,4 @@
+mod appearance;
 mod archive;
 mod bookmark;
 mod command;
@@ -23,6 +24,7 @@ mod tab_group;
 mod update;
 mod url_text;
 
+pub use appearance::{AppearanceSettings, ThemeMode, WallpaperTheme};
 pub use archive::{ArchiveSource, ArchivedTab};
 pub use bookmark::BookmarkEntry;
 pub use command::{CommandIntent, CommandScope};