fix: pre-fetch bincio wheel via RN networking to avoid ATS blocking HTTP in WKWebView

WKWebView blocks HTTP requests (ATS) even when NSAllowsLocalNetworking is set for
the app's own networking — so fetch(http://192.168.x.x/api/wheel/download) inside
the WebView always fails with 'Load failed' on iOS.

- extractActivity.ts: rename wheelUrl param to wheelBase64; WebView now receives
  the wheel as pre-fetched base64 bytes rather than a URL to fetch itself
- PyodideWebView.tsx: decode wheelBase64 → Uint8Array → Blob → blob URL for
  micropip.install; fix baseUrl '' → 'https://localhost' (null origin blocks fetch
  on iOS)
- import.tsx: add fetchWheelBase64() that resolves the wheel URL via
  /api/wheel/version then fetches with native networking (HTTP works); caches
  result in memory so repeated imports in one session don't re-download

mobile/extraction/PyodideWebView.tsx

@@ -87,10 +87,10 @@ var initError     = null;
 })();
 
 window._bincioExtract = async function(params) {
-  var reqId    = params.reqId;
-  var filename = params.filename;
-  var base64   = params.base64;
-  var wheelUrl = params.wheelUrl;
+  var reqId       = params.reqId;
+  var filename    = params.filename;
+  var base64      = params.base64;
+  var wheelBase64 = params.wheelBase64;  // pre-fetched by React Native (avoids ATS/HTTP issues)
 
   function post(m) { _post(Object.assign({}, m, { reqId: reqId })); }
 
@@ -108,13 +108,14 @@ window._bincioExtract = async function(params) {
     }
     if (initError) throw new Error(initError);
 
-    // Install bincio wheel on first extraction (lazy: keeps startup fast)
+    // Install bincio wheel on first extraction.
+    // Wheel bytes arrive pre-fetched from the React Native side as base64,
+    // so the WebView never needs to make an HTTP request (avoids ATS blocks).
     if (!wheelReady) {
       post({ type: 'progress', msg: 'Loading Bincio…' });
-      var resp = await fetch(wheelUrl);
-      if (!resp.ok) throw new Error('Failed to fetch Bincio wheel (' + resp.status + ')');
-      var wheelBlob = new Blob([await resp.arrayBuffer()]);
-      var blobUrl   = URL.createObjectURL(wheelBlob);
+      var wheelBytes = Uint8Array.from(atob(wheelBase64), function(c) { return c.charCodeAt(0); });
+      var wheelBlob  = new Blob([wheelBytes]);
+      var blobUrl    = URL.createObjectURL(wheelBlob);
       pyodide.globals.set('_blobUrl', blobUrl);
       await pyodide.runPythonAsync(_PY_INSTALL_WHEEL);
       URL.revokeObjectURL(blobUrl);
@@ -158,7 +159,7 @@ export function PyodideWebView() {
   return (
     <WebView
       ref={pyodideRef}
-      source={{ html: PYODIDE_HTML, baseUrl: '' }}
+      source={{ html: PYODIDE_HTML, baseUrl: 'https://localhost' }}
       style={styles.hidden}
       onMessage={handleWebViewMessage}
       javaScriptEnabled

mobile/extraction/extractActivity.ts

@@ -54,10 +54,12 @@ export function handleWebViewMessage(e: WebViewMessageEvent): void {
   }
 }
 
+// wheelBase64 is the bincio .whl file pre-fetched by the React Native side
+// (native networking supports HTTP on local network; WKWebView does not).
 export function extractFile(
   filename: string,
   base64: string,
-  wheelUrl: string,
+  wheelBase64: string,
   onStatus: (msg: string) => void = () => {},
 ): Promise<ExtractionResult> {
   if (isExtracting) return Promise.reject(new Error('Another extraction is already in progress'));
@@ -67,7 +69,7 @@ export function extractFile(
 
   isExtracting = true;
   const reqId = String(++reqCounter);
-  const args = JSON.stringify({ reqId, filename, base64, wheelUrl });
+  const args = JSON.stringify({ reqId, filename, base64, wheelBase64 });
 
   return new Promise<ExtractionResult>((resolve, reject) => {
     pending.set(reqId, {