fix(review): bugs, arch violations, design smells

P1 bugs:
- unix_launcher: shell_split respects quoted args (was split_whitespace)
- plugin-host: 5s timeout on external plugin search
- ui: handle engine init panic, wire error state
- ui-egui: read window config instead of always using defaults
- plugin-url: use OpenPath action instead of SpawnProcess+xdg-open

Architecture:
- remove WindowConfig (mirror of WindowCfg); use WindowCfg directly
- remove on_select closure from SearchResult (domain leakage)
- remove LaunchAction::Custom; add Plugin::on_selected + SearchEngine::on_selected
- apps: record frecency via on_selected instead of embedded closure

Design smells:
- frecency: extract decay_factor helper, write outside mutex
- apps: remove cfg(test) cache_path hack; add new_for_test ctor
- apps: stable ResultId using name+exec to prevent collision
- files: stable ResultId using full path instead of index
- plugin-host: remove k-launcher-os-bridge dep (WindowConfig gone)

crates/k-launcher-ui-egui/src/app.rs

@@ -2,7 +2,6 @@ use std::sync::{Arc, mpsc};
 
 use egui::{Color32, Key, ViewportCommand};
 use k_launcher_kernel::{AppLauncher, SearchEngine, SearchResult};
-use k_launcher_os_bridge::WindowConfig;
 
 const BG: Color32 = Color32::from_rgba_premultiplied(20, 20, 30, 230);
 const BORDER_COLOR: Color32 = Color32::from_rgb(229, 125, 33);
@@ -83,9 +82,7 @@ impl eframe::App for KLauncherApp {
 
         if launch_selected {
             if let Some(result) = self.results.get(self.selected) {
-                if let Some(on_select) = &result.on_select {
-                    on_select();
-                }
+                self.engine.on_selected(&result.id);
                 self.launcher.execute(&result.action);
             }
             ctx.send_viewport_cmd(ViewportCommand::Close);
@@ -166,17 +163,17 @@ impl eframe::App for KLauncherApp {
 pub fn run(
     engine: Arc<dyn SearchEngine>,
     launcher: Arc<dyn AppLauncher>,
+    window_cfg: &k_launcher_config::WindowCfg,
 ) -> Result<(), eframe::Error> {
-    let wc = WindowConfig::from_cfg(&k_launcher_config::WindowCfg::default());
     let rt = tokio::runtime::Runtime::new().expect("tokio runtime");
     let handle = rt.handle().clone();
 
     let options = eframe::NativeOptions {
         viewport: egui::ViewportBuilder::default()
-            .with_inner_size([wc.width, wc.height])
-            .with_decorations(wc.decorations)
-            .with_transparent(wc.transparent)
-            .with_resizable(wc.resizable)
+            .with_inner_size([window_cfg.width, window_cfg.height])
+            .with_decorations(window_cfg.decorations)
+            .with_transparent(window_cfg.transparent)
+            .with_resizable(window_cfg.resizable)
             .with_always_on_top(),
         ..Default::default()
     };

crates/k-launcher-ui-egui/src/lib.rs

@@ -7,6 +7,7 @@ use k_launcher_kernel::{AppLauncher, SearchEngine};
 pub fn run(
     engine: Arc<dyn SearchEngine>,
     launcher: Arc<dyn AppLauncher>,
+    window_cfg: &k_launcher_config::WindowCfg,
 ) -> Result<(), eframe::Error> {
-    app::run(engine, launcher)
+    app::run(engine, launcher, window_cfg)
 }