feat(companion): native wallet QR scanner, gesture hint overlay, WebView file uploads

- WalletQrScannerModal: native CameraX+zxing scanner styled like the web
  wallet modal, with an upload-image decode path; opened by the web UI
  through the new window.ArchipelagoQr JS bridge. Decodes stream back via
  window.__archyQrResult; the page mirrors status lines out and closes
  the modal when it accepts a code. Detection/spend logic stays in the
  web modal.
- onShowFileChooser: <input type=file> was silently ignored by the
  WebView — file pickers (incl. the wallet's upload option) now work.
- GestureHintOverlay: one-time animation teaching the three-finger hold,
  armed ~2 minutes after login (gesture_hint_seen flag).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Android/app/src/main/res/values/strings.xml

@@ -41,4 +41,11 @@
     <string name="edit_server_title">Edit Server</string>
     <string name="save_changes">Save Changes</string>
     <string name="cancel">Cancel</string>
+    <string name="gesture_hint_title">Hold with three fingers</string>
+    <string name="gesture_hint_body">Anywhere in the app — opens the remote control and menu</string>
+    <string name="gesture_hint_got_it">Got it</string>
+    <string name="scan_to_send">Scan to send</string>
+    <string name="scan_wallet_hint">Point the camera at a Lightning invoice, Bitcoin address, Cashu or Fedimint code</string>
+    <string name="upload_qr_image">Upload image</string>
+    <string name="no_qr_in_image">No QR code found in that image — try another, closer and well-lit</string>
 </resources>