fix: Windows Claude CLI path discovery and Extensions scroll

- Fix Windows Claude CLI not found when installed as .exe or without
  extension in .local\bin (closes #6). Now searches all extensions
  (.cmd, .exe, .bat, and bare) for every candidate directory.
- Fix Extensions/Skills list not scrollable when many items exist.
  Change content container to overflow-hidden so internal ScrollArea
  works correctly. Add overflow-auto to McpManager for its own scroll.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/plugins/McpManager.tsx

@@ -136,7 +136,7 @@ export function McpManager() {
   const serverCount = Object.keys(servers).length;
 
   return (
-    <div>
+    <div className="h-full overflow-auto">
       <div className="flex items-center justify-between mb-4">
         <div>
           <div className="flex items-center gap-2">