refactor: cleanup and minor improvements

- Remove unused useDarkMode hook (now using shadcn theme-provider)
- Clean up MCP components (remove redundant code)
- Add restart API to settings
- Minor type improvements

src/lib/api/settings.ts

@@ -98,6 +98,15 @@ export const settingsApi = {
   },
 
   async openExternal(url: string): Promise<void> {
+    try {
+      const u = new URL(url);
+      const scheme = u.protocol.replace(":", "").toLowerCase();
+      if (scheme !== "http" && scheme !== "https") {
+        throw new Error("Unsupported URL scheme");
+      }
+    } catch {
+      throw new Error("Invalid URL");
+    }
     await invoke("open_external", { url });
   },
 };