feat: restructure k-launcher workspace and add core functionality

- Updated Cargo.toml to include a new k-launcher crate and reorganized workspace members.
- Introduced a README.md file detailing the project philosophy, architecture, and technical specifications.
- Implemented a new Kernel struct in k-launcher-kernel for managing plugins and search functionality.
- Created a Plugin trait for plugins to implement, allowing for asynchronous search operations.
- Developed k-launcher-ui with an Iced-based UI for user interaction, including search input and result display.
- Added AppsPlugin and CalcPlugin to handle application launching and basic calculations, respectively.
- Established a theme module for UI styling, focusing on an Aero aesthetic.
- Removed unnecessary main.rs files from plugin crates, streamlining the project structure.

crates/k-launcher-kernel/src/lib.rs

@@ -1,14 +1,168 @@
-pub fn add(left: u64, right: u64) -> u64 {
-    left + right
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use futures::future::join_all;
+
+pub type PluginName = &'static str;
+
+// --- Newtypes ---
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+pub struct ResultId(String);
+
+impl ResultId {
+    pub fn new(id: impl Into<String>) -> Self {
+        Self(id.into())
+    }
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+pub struct ResultTitle(String);
+
+impl ResultTitle {
+    pub fn new(title: impl Into<String>) -> Self {
+        Self(title.into())
+    }
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, serde::Serialize, serde::Deserialize)]
+pub struct Score(u32);
+
+impl Score {
+    pub fn new(value: u32) -> Self {
+        Self(value)
+    }
+    pub fn value(self) -> u32 {
+        self.0
+    }
+}
+
+// --- SearchResult ---
+
+pub struct SearchResult {
+    pub id: ResultId,
+    pub title: ResultTitle,
+    pub description: Option<String>,
+    pub icon: Option<String>,
+    pub score: Score,
+    pub on_execute: Arc<dyn Fn() + Send + Sync>,
+}
+
+impl std::fmt::Debug for SearchResult {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("SearchResult")
+            .field("id", &self.id)
+            .field("title", &self.title)
+            .field("icon", &self.icon)
+            .field("score", &self.score)
+            .finish_non_exhaustive()
+    }
+}
+
+// --- Plugin trait ---
+
+#[async_trait]
+pub trait Plugin: Send + Sync {
+    fn name(&self) -> PluginName;
+    async fn search(&self, query: &str) -> Vec<SearchResult>;
+}
+
+// --- Kernel (Application use case) ---
+
+pub struct Kernel {
+    plugins: Vec<Arc<dyn Plugin>>,
+}
+
+impl Kernel {
+    pub fn new(plugins: Vec<Arc<dyn Plugin>>) -> Self {
+        Self { plugins }
+    }
+
+    pub async fn search(&self, query: &str) -> Vec<SearchResult> {
+        let futures = self.plugins.iter().map(|p| p.search(query));
+        let nested: Vec<Vec<SearchResult>> = join_all(futures).await;
+        let mut flat: Vec<SearchResult> = nested.into_iter().flatten().collect();
+        flat.sort_by(|a, b| b.score.cmp(&a.score));
+        flat
+    }
+}
+
+// --- Tests ---
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    struct MockPlugin {
+        results: Vec<(&'static str, u32)>,
+    }
+
+    impl MockPlugin {
+        fn returns(results: Vec<(&'static str, u32)>) -> Self {
+            Self { results }
+        }
+    }
+
+    #[async_trait]
+    impl Plugin for MockPlugin {
+        fn name(&self) -> PluginName {
+            "mock"
+        }
+
+        async fn search(&self, _query: &str) -> Vec<SearchResult> {
+            self.results
+                .iter()
+                .enumerate()
+                .map(|(i, (title, score))| SearchResult {
+                    id: ResultId::new(format!("id-{i}")),
+                    title: ResultTitle::new(*title),
+                    description: None,
+                    icon: None,
+                    score: Score::new(*score),
+                    on_execute: Arc::new(|| {}),
+                })
+                .collect()
+        }
+    }
+
     #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
+    fn newtype_result_id() {
+        assert_eq!(ResultId::new("x").as_str(), "x");
+    }
+
+    #[test]
+    fn newtype_score() {
+        assert_eq!(Score::new(42).value(), 42);
+    }
+
+    #[test]
+    fn newtype_title() {
+        assert_eq!(ResultTitle::new("hello").as_str(), "hello");
+    }
+
+    #[tokio::test]
+    async fn empty_kernel_returns_empty() {
+        let k = Kernel::new(vec![]);
+        assert!(k.search("x").await.is_empty());
+    }
+
+    #[tokio::test]
+    async fn kernel_sorts_by_score_desc() {
+        let plugin = Arc::new(MockPlugin::returns(vec![
+            ("lower", 5),
+            ("higher", 10),
+            ("middle", 7),
+        ]));
+        let k = Kernel::new(vec![plugin]);
+        let results = k.search("q").await;
+        assert_eq!(results[0].score.value(), 10);
+        assert_eq!(results[1].score.value(), 7);
+        assert_eq!(results[2].score.value(), 5);
     }
 }