drop python backend layer

frontend/src/lib/project.ts

@@ -1,3 +1,5 @@
+import { renderKeyboardTrack } from './audio/export';
+import type { SampleCache } from './audio/sampleCache';
 import type { LegacySwitchType, Marker, Project, SwitchType } from './types';
 import { app, setActiveSwitch, setMarkers, setSelectedIds } from './store.svelte';
 
@@ -50,24 +52,19 @@ export function loadProject(data: Project & { version?: number; switch?: string
   setSelectedIds(new Set());
 }
 
-export async function exportAudio(duration: number) {
+/**
+ * Export keyboard SFX only as a WAV file (no video audio).
+ * Rendered client-side at 1× via OfflineAudioContext.
+ */
+export async function exportAudio(duration: number, cache?: SampleCache) {
   const project = buildProject();
-  const response = await fetch('/api/export/audio', {
-    method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify({
-      duration,
-      switch: project.switch,
-      markers: project.markers,
-    }),
+  const blob = await renderKeyboardTrack({
+    duration,
+    switchType: project.switch,
+    markers: project.markers,
+    cache,
   });
 
-  if (!response.ok) {
-    const detail = await response.text();
-    throw new Error(detail || 'Audio export failed');
-  }
-
-  const blob = await response.blob();
   const url = URL.createObjectURL(blob);
   const anchor = document.createElement('a');
   anchor.href = url;