fix: Remove duplicate routing, fix example patterns

Fixes 4 bug patterns:

1. Write-without-read: main.tsx stored patterns in sessionStorage
   but nothing read them. Fixed by removing the broken Router.

2. Dead code: main.tsx Router duplicated App.tsx's landing page
   logic. Removed - App.tsx handles all routing internally.

3. Full page reload: main.tsx used window.location.href which
   caused unnecessary reloads. App.tsx uses React state transitions.

4. Invalid sample ID: LANDING_SAMPLES used 'perc' which doesn't
   exist. Changed to 'clap' (a valid sample ID).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: adewale

app/src/App.tsx

@@ -543,7 +543,8 @@ function hasSessionInUrl(): boolean {
 }
 
 // Default drum samples for landing page example patterns
-const LANDING_SAMPLES = ['kick', 'snare', 'hihat', 'perc'];
+// Must match valid sample IDs from sample-constants.ts
+const LANDING_SAMPLES = ['kick', 'snare', 'hihat', 'clap'];
 
 function App() {
   const [showLanding, setShowLanding] = useState(() => !hasSessionInUrl());

app/src/main.tsx

@@ -1,8 +1,7 @@
-import { StrictMode, useState, useEffect, useCallback } from 'react'
+import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import './index.css'
 import App from './App.tsx'
-import { LandingPage } from './components/LandingPage'
 
 // Initialize unified debugging infrastructure
 // The debug coordinator handles URL flags (?debug=1, ?trace=1, etc.)
@@ -16,62 +15,15 @@ if (import.meta.env.DEV) {
 }
 
 /**
- * Root Router Component
+ * App handles all routing internally:
+ * - "/" shows LandingPage (showLanding = true)
+ * - "/s/{id}" shows session UI (showLanding = false)
  *
- * Handles routing between LandingPage and App:
- * - "/" shows LandingPage
- * - "/s/{uuid}" shows App with session
- *
- * @see /specs/LANDING-PAGE.md for routing specification
+ * This avoids the full page reload that window.location.href causes.
+ * App.tsx uses React state transitions for instant navigation.
  */
-function Router() {
-  const [showApp, setShowApp] = useState(false);
-
-  useEffect(() => {
-    const path = window.location.pathname;
-
-    // Check for session URL pattern: /s/{uuid}
-    // UUIDs are 36 characters: 8-4-4-4-12 hex digits
-    const sessionMatch = path.match(/^\/s\/([a-f0-9-]{36})$/i);
-    if (sessionMatch) {
-      setShowApp(true);
-      return;
-    }
-
-    // Any other path with /s/ prefix should show the app
-    // (handles partial UUIDs, session not found, etc.)
-    if (path.startsWith('/s/')) {
-      setShowApp(true);
-      return;
-    }
-
-    // Root path or unknown paths show landing page
-    // Landing page is the default
-  }, []);
-
-  // Start a new session from landing page
-  const handleStartSession = useCallback(() => {
-    // Navigate to create a new session
-    // The App component will handle creating a new session on mount
-    window.location.href = '/s/new';
-  }, []);
-
-  // Select an example pattern - navigate to app with pattern in URL state
-  const handleSelectExample = useCallback((pattern: number[][], bpm: number) => {
-    // Store example in sessionStorage for App to pick up
-    sessionStorage.setItem('pendingExample', JSON.stringify({ pattern, bpm }));
-    window.location.href = '/s/new';
-  }, []);
-
-  if (showApp) {
-    return <App />;
-  }
-
-  return <LandingPage onStartSession={handleStartSession} onSelectExample={handleSelectExample} />;
-}
-
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <Router />
+    <App />
   </StrictMode>,
 )