Add theme-aware notification cards with grouped popup stacks

crates/ferese-core/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod desktop;
+pub mod notifications;
 mod output;
 mod workspace;
 

crates/ferese-core/src/notifications.rs

@@ -0,0 +1,28 @@
+use serde::Deserialize;
+
+#[derive(Clone, Debug, Deserialize, PartialEq, Eq)]
+#[serde(default, deny_unknown_fields)]
+pub struct NotificationConfig {
+    pub show_popups: bool,
+    pub do_not_disturb: bool,
+    pub timeout_ms: u32,
+}
+
+impl Default for NotificationConfig {
+    fn default() -> Self {
+        Self {
+            show_popups: true,
+            do_not_disturb: false,
+            timeout_ms: 6000,
+        }
+    }
+}
+
+impl NotificationConfig {
+    pub fn validate(&self) -> Result<(), String> {
+        if !(1000..=30000).contains(&self.timeout_ms) {
+            return Err("notifications.timeout_ms must be between 1000 and 30000".into());
+        }
+        Ok(())
+    }
+}