fix: move PyodideWebView into Import tab; fix micropip blob URL error

Layout fix: WebView as a sibling in the root layout breaks flex geometry even
with position:absolute. Moving it inside the Import tab screen (which Expo Router
keeps mounted after first visit) eliminates the issue entirely and restores the
original simple root layout.

micropip fix: blob: URLs are not a recognised scheme in micropip — they are parsed
as package requirement strings, producing InvalidRequirement. Write the wheel bytes
to Pyodide's Emscripten FS (/tmp/bincio.whl) and install via emfs:/// instead.

mobile/app/(tabs)/import.tsx

@@ -2,8 +2,9 @@ import * as DocumentPicker from 'expo-document-picker';
 import * as FileSystem from 'expo-file-system/legacy';
 import { useSQLiteContext } from 'expo-sqlite';
 import { useState } from 'react';
-import { Alert, Pressable, ScrollView, StyleSheet, Text, View } from 'react-native';
+import { Pressable, ScrollView, StyleSheet, Text, View } from 'react-native';
 import { insertActivity } from '@/db/queries';
+import { PyodideWebView } from '@/extraction/PyodideWebView';
 import { extractFile } from '@/extraction/extractActivity';
 
 const FIT_EXTENSIONS  = ['.fit', '.fit.gz'];
@@ -129,6 +130,13 @@ export default function ImportScreen() {
   }
 
   return (
+    <View style={styles.screen}>
+      {/* Hidden WebView for Pyodide — mounted here so it lives inside the tab
+          (Expo Router keeps tabs mounted after first visit, preserving Pyodide state).
+          The 1×1 container clips it out of the scroll layout entirely. */}
+      <View style={styles.hiddenEngine}>
+        <PyodideWebView />
+      </View>
     <ScrollView style={styles.container} contentContainerStyle={styles.content}>
       <Text style={styles.header}>Import</Text>
 
@@ -192,6 +200,7 @@ export default function ImportScreen() {
         </Text>
       </View>
     </ScrollView>
+    </View>
   );
 }
 
@@ -246,7 +255,9 @@ function arrayBufferToBase64(buf: ArrayBuffer): string {
 // ── Styles ───────────────────────────────────────────────────────────────────
 
 const styles = StyleSheet.create({
-  container: { flex: 1, backgroundColor: '#09090b' },
+  screen:       { flex: 1, backgroundColor: '#09090b' },
+  hiddenEngine: { position: 'absolute', width: 1, height: 1, overflow: 'hidden' },
+  container: { flex: 1 },
   content:   { padding: 16, paddingTop: 60, paddingBottom: 40 },
   header:    { color: '#fff', fontSize: 22, fontWeight: '700', marginBottom: 12 },
   body:      { color: '#a1a1aa', fontSize: 14, lineHeight: 20, marginBottom: 24 },