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/plugins/plugin-calc/src/lib.rs

@@ -0,0 +1,83 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use k_launcher_kernel::{Plugin, PluginName, ResultId, ResultTitle, Score, SearchResult};
+
+pub struct CalcPlugin;
+
+impl CalcPlugin {
+    pub fn new() -> Self {
+        Self
+    }
+}
+
+impl Default for CalcPlugin {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+fn should_eval(query: &str) -> bool {
+    query
+        .chars()
+        .next()
+        .map(|c| c.is_ascii_digit() || c == '(' || c == '-')
+        .unwrap_or(false)
+        || query.starts_with('=')
+}
+
+#[async_trait]
+impl Plugin for CalcPlugin {
+    fn name(&self) -> PluginName {
+        "calc"
+    }
+
+    async fn search(&self, query: &str) -> Vec<SearchResult> {
+        if !should_eval(query) {
+            return vec![];
+        }
+        let expr = query.strip_prefix('=').unwrap_or(query);
+        match evalexpr::eval_number(expr) {
+            Ok(n) if n.is_finite() => {
+                let display = if n.fract() == 0.0 {
+                    format!("= {}", n as i64)
+                } else {
+                    format!("= {n}")
+                };
+                vec![SearchResult {
+                    id: ResultId::new("calc-result"),
+                    title: ResultTitle::new(display),
+                    description: None,
+                    icon: None,
+                    score: Score::new(90),
+                    on_execute: Arc::new(|| {}),
+                }]
+            }
+            _ => vec![],
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn calc_valid_expr() {
+        let p = CalcPlugin::new();
+        let results = p.search("2+2").await;
+        assert_eq!(results[0].title.as_str(), "= 4");
+    }
+
+    #[tokio::test]
+    async fn calc_non_numeric_returns_empty() {
+        let p = CalcPlugin::new();
+        assert!(p.search("firefox").await.is_empty());
+    }
+
+    #[tokio::test]
+    async fn calc_bad_expr_returns_empty() {
+        let p = CalcPlugin::new();
+        assert!(p.search("1/0").await.is_empty());
+    }
+}

crates/plugins/plugin-calc/src/main.rs

@@ -1,3 +1 @@
-fn main() {
-    println!("Hello, world!");
-}
+fn main() {}