A Mirror window for sketch entities, holding both picks until OK (#734)

Sketch Mirror now opens a tool window with Entities and Mirror line inputs, so both picks stay visible and editable until OK, replacing the old click-then-right-click flow.

crates/ui-egui/src/locales/ko.json

@@ -196,6 +196,7 @@
   "ui.measure": "측정",
   "ui.midpoint": "중간점",
   "ui.mirror": "대칭 복사",
+  "ui.mirror_line": "대칭선",
   "ui.modify": "수정",
   "ui.move": "이동",
   "ui.multiple": "다중",