Reset the custom watermark when returning to the camera

The mark is placed against the library photo it was dragged on, but it
survived the switch to the live camera: the preview kept drawing it and
the next capture burned it in. Camera mode already drops the frame and
the library GPS for the same reason, so drop the accepted watermark too.

Resetting both the draft and the accepted copy keeps the chip honest and
stops the AsyncStorage session snapshot from restoring a camera mode
that still carries a library watermark.

App.tsx

@@ -850,6 +850,13 @@ export default function App() {
     // picker to undo it, so it must never follow the user onto the live camera
     // (and into the capture, which burns the frame in).
     if (next === 'camera') setSelectedFrame('none');
+    // Same for the custom watermark: it was placed against THAT library photo,
+    // so it must not follow the user onto the live camera either — the mark
+    // goes back to off, and re-enabling + editing it is a deliberate choice.
+    if (next === 'camera') {
+      setCustomWm({ ...DEFAULT_CUSTOM_WM });
+      setCustomWmApplied({ ...DEFAULT_CUSTOM_WM });
+    }
     setMode(next);
   };