fix(terminal): resolve PTY shell exec error, simplify CLI, unify Config tabs, restore Studio CSS

- Fix detectShell() to return full paths via LookPath (was returning bare
  names causing exec error on some systems)
- Add shell path validation before pty.Start to prevent crashes
- Simplify CLI: remove all subcommands, keep only desktop launch with --port
- Restore missing Studio shared CSS (code blocks, input area, animations)
- Replace Config vertical sidebar with horizontal nav-tabs matching main layout

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/src/components/Config.jsx

@@ -132,27 +132,23 @@ export default function Config({ api }) {
     <div className="config-window">
       {toast && <div className="config-toast">{toast}</div>}
 
-      <div className="config-sidebar">
+      <div className="config-tabs-bar">
         {PANELS.map(p => {
           const Icon = p.icon
           return (
             <div
               key={p.id}
-              className={`config-sidebar-item ${activePanel === p.id ? 'active' : ''}`}
+              className={`nav-tab ${activePanel === p.id ? 'active' : ''}`}
               onClick={() => setActivePanel(p.id)}
             >
-              <Icon size={16} />
-              <span>{t(`config.panels.${p.id}`)}</span>
+              <span className="tab-icon"><Icon size={15} /></span>
+              {t(`config.panels.${p.id}`)}
             </div>
           )
         })}
       </div>
 
       <div className="config-panel-area">
-        <div className="config-panel-header">
-          <h2 className="config-panel-title">{t(`config.panels.${activePanel}`)}</h2>
-        </div>
-
         <div className="config-panel-body">
           {activePanel === 'profile' && (
             <PanelProfile