fix: pass wheel filename through extraction chain to fix micropip install

micropip requires the full PEP 427 wheel filename (name-version-py-abi-plat.whl)
— writing the file as bincio.whl caused InvalidWheelFilename. The wheel URL from
/api/wheel/version now provides the basename; it flows through fetchWheelBase64 →
extractFile → WebView where the file is written with the correct name and
_wheel_path is set as a Pyodide global before PY_INSTALL_WHEEL runs.

mobile/app/(tabs)/import.tsx

@@ -97,12 +97,13 @@ export default function ImportScreen() {
     // allows local-network HTTP (NSAllowsLocalNetworking=true in Info.plist).
     const instanceUrl = await getInstanceUrl(dbCtx);
     setState({ status: 'loading', msg: 'Fetching Bincio engine…' });
-    const wheelBase64 = await fetchWheelBase64(instanceUrl);
+    const { base64: wheelBase64, filename: wheelFilename } = await fetchWheelBase64(instanceUrl);
 
     const result = await extractFile(
       name,
       base64,
       wheelBase64,
+      wheelFilename,
       (msg) => setState({ status: 'loading', msg }),
     );
 
@@ -215,21 +216,25 @@ async function getInstanceUrl(db: ReturnType<typeof useSQLiteContext>): Promise<
 }
 
 // In-memory cache so repeated imports in one session don't re-download the wheel.
-let _cachedWheelBase64: string | null = null;
+let _cachedWheel: { base64: string; filename: string } | null = null;
 
-async function fetchWheelBase64(instanceUrl: string): Promise<string> {
-  if (_cachedWheelBase64) return _cachedWheelBase64;
+async function fetchWheelBase64(instanceUrl: string): Promise<{ base64: string; filename: string }> {
+  if (_cachedWheel) return _cachedWheel;
 
   const base = instanceUrl || 'https://bincio.org';
 
   // Ask the instance for the canonical wheel URL (handles both dev and prod layouts).
   let wheelUrl = `${base}/api/wheel/download`;
+  let wheelFilename = 'bincio-0.1.0-py3-none-any.whl';
   try {
     const vr = await fetch(`${base}/api/wheel/version`, { signal: AbortSignal.timeout(5000) });
     if (vr.ok) {
       const d = await vr.json() as { api_url?: string; url?: string };
       const path = d.api_url ?? d.url ?? '/api/wheel/download';
       wheelUrl = path.startsWith('http') ? path : `${base}${path}`;
+      // Extract the filename from the URL path (last segment after final /)
+      const urlBasename = wheelUrl.split('/').pop() ?? '';
+      if (urlBasename.endsWith('.whl')) wheelFilename = urlBasename;
     }
   } catch {}
 
@@ -237,8 +242,8 @@ async function fetchWheelBase64(instanceUrl: string): Promise<string> {
   const resp = await fetch(wheelUrl);
   if (!resp.ok) throw new Error(`Could not download Bincio engine (${resp.status}). Is the instance running?`);
   const buf = await resp.arrayBuffer();
-  _cachedWheelBase64 = arrayBufferToBase64(buf);
-  return _cachedWheelBase64;
+  _cachedWheel = { base64: arrayBufferToBase64(buf), filename: wheelFilename };
+  return _cachedWheel;
 }
 
 function arrayBufferToBase64(buf: ArrayBuffer): string {