feat: Phase 1 — FIT/GPX/TCX extraction via Pyodide in hidden WebView

- extraction/PyodideWebView.tsx: hidden WebView (1×1 px, off-screen) that
  bootstraps Pyodide v0.26.4 from jsDelivr CDN on app startup; loads lxml,
  pyyaml, micropip, fitdecode, gpxpy automatically; installs the bincio wheel
  lazily on the first extraction call via a blob URL (avoids startup delay)
- extraction/extractActivity.ts: typed bridge — extractFile(filename, base64,
  wheelUrl, onStatus) injects JS into the WebView, tracks pending promises by
  request ID, resolves with { id, detail, timeseries, geojson, sourceHash }
- app/_layout.tsx: mounts <PyodideWebView> outside SQLiteProvider at root so
  the runtime warms up as soon as the app opens
- app/(tabs)/import.tsx: replaces the placeholder alert with real extraction;
  reads files as base64, calls extractFile with a progress callback, stores
  detail_json + timeseries_json + geojson + real SHA-256 source_hash; resolves
  wheel URL via GET /api/wheel/version with fallback to /api/wheel/download;
  falls back to bincio.org if no instance is configured

mobile/extraction/extractActivity.ts

@@ -0,0 +1,80 @@
+import { createRef } from 'react';
+import type WebView from 'react-native-webview';
+import type { WebViewMessageEvent } from 'react-native-webview';
+
+export type ExtractionResult = {
+  id: string;
+  detail: object;
+  timeseries: object | null;
+  geojson: object | null;
+  sourceHash: string;
+};
+
+type Pending = {
+  resolve: (r: ExtractionResult) => void;
+  reject: (e: Error) => void;
+  onStatus: (msg: string) => void;
+};
+
+export const pyodideRef = createRef<WebView>();
+
+const pending = new Map<string, Pending>();
+let reqCounter = 0;
+let isExtracting = false;
+
+export function handleWebViewMessage(e: WebViewMessageEvent): void {
+  let msg: Record<string, unknown>;
+  try { msg = JSON.parse(e.nativeEvent.data); } catch { return; }
+
+  const reqId = msg.reqId as string | undefined;
+  const p = reqId ? pending.get(reqId) : undefined;
+
+  switch (msg.type) {
+    case 'result':
+      if (p) {
+        pending.delete(reqId!);
+        p.resolve({
+          id: msg.id as string,
+          detail: msg.detail as object,
+          timeseries: (msg.timeseries as object | null) ?? null,
+          geojson: (msg.geojson as object | null) ?? null,
+          sourceHash: msg.sourceHash as string,
+        });
+      }
+      break;
+    case 'error':
+      if (p) {
+        pending.delete(reqId!);
+        p.reject(new Error(msg.message as string));
+      }
+      break;
+    case 'progress':
+      p?.onStatus(msg.msg as string);
+      break;
+  }
+}
+
+export function extractFile(
+  filename: string,
+  base64: string,
+  wheelUrl: string,
+  onStatus: (msg: string) => void = () => {},
+): Promise<ExtractionResult> {
+  if (isExtracting) return Promise.reject(new Error('Another extraction is already in progress'));
+
+  const webview = pyodideRef.current;
+  if (!webview) return Promise.reject(new Error('Extraction engine not ready — restart the app'));
+
+  isExtracting = true;
+  const reqId = String(++reqCounter);
+  const args = JSON.stringify({ reqId, filename, base64, wheelUrl });
+
+  return new Promise<ExtractionResult>((resolve, reject) => {
+    pending.set(reqId, {
+      resolve: (r) => { isExtracting = false; resolve(r); },
+      reject: (e) => { isExtracting = false; reject(e); },
+      onStatus,
+    });
+    webview.injectJavaScript(`window._bincioExtract(${args}); true;`);
+  });
+}