fix(mobile): patch pyodide.js at runtime to bypass Chrome 61 import() syntax

Chrome 61 (Karoo WebView) cannot parse dynamic import() — a SyntaxError at
parse time prevents loadPyodide from ever being defined.

Fix: fetch pyodide.js as text, replace every import( with a __loadScript(
shim that uses <script> tag injection, then inject via Blob URL. The Blob
script is never pre-scanned for module syntax so the patch is invisible to
the parser.

Also: expose waitForEngine() from extractActivity so callers can await
engine readiness before batching files — manual scan now shows "Preparing
extraction engine…" instead of flooding with N individual failures.

mobile/app/(tabs)/import.tsx

@@ -6,7 +6,7 @@ import { useCallback, useEffect, useRef, useState } from 'react';
 import { AppState, PermissionsAndroid, Platform, Pressable, ScrollView, StyleSheet, Text, View } from 'react-native';
 import { insertActivity, isSourcePathImported, getSetting } from '@/db/queries';
 import { PyodideWebView } from '@/extraction/PyodideWebView';
-import { extractFile } from '@/extraction/extractActivity';
+import { extractFile, waitForEngine } from '@/extraction/extractActivity';
 import { useTheme } from '@/ThemeContext';
 
 const FIT_EXTENSIONS   = ['.fit', '.fit.gz'];
@@ -54,7 +54,10 @@ export default function ImportScreen() {
     const path = await getSetting(db, 'auto_import_path');
     if (!path) return;
     const instanceUrl = await getSetting(db, 'instance_url');
-    if (!instanceUrl) return; // silently skip — engine can't be downloaded without an instance
+    if (!instanceUrl) return;
+
+    // Wait for the extraction engine — but don't block forever on auto-scan.
+    try { await waitForEngine(120_000); } catch { return; }
 
     const newFiles = await discoverNewFiles(db, path);
     if (newFiles.length === 0) return;
@@ -77,6 +80,14 @@ export default function ImportScreen() {
       return;
     }
 
+    setState({ status: 'loading', msg: 'Preparing extraction engine…', current: 0, total: 0 });
+    try {
+      await waitForEngine();
+    } catch (e: unknown) {
+      setState({ status: 'error', message: e instanceof Error ? e.message : String(e) });
+      return;
+    }
+
     setState({ status: 'loading', msg: 'Scanning…', current: 0, total: 0 });
     const newFiles = await discoverNewFiles(db, path);
     if (newFiles.length === 0) {