First F-Droid release.

* Polygon tessellation editor wrapped as a native WebView app.
* Create tilings from a palette or by clicking edges, with live validation.
* Add Copy under a plane isometry (translate, rotate, reflect, glide reflect) with anchor snapping.
* Eraser, interior insertion, selection by colour/shape, colour picker.
* Pan, zoom, rotate; export to SVG and DOT.
* Fully offline: no network, no accounts, no trackers.
