feat: scene traps, material legends, and scene editor window

Add trap overlays with session state, material legend editor/panel, and a dedicated scene editor window wired through IPC and project persistence.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/renderer/shared/materials/MaterialOverlay.module.css

@@ -50,15 +50,33 @@
 
 .image {
   position: absolute;
-  left: 50%;
-  top: 50%;
+  inset: 0;
+  width: 100%;
+  height: 100%;
   display: block;
   object-fit: fill;
   border-radius: 6px;
   box-shadow: 0 18px 48px rgba(0, 0, 0, 0.55);
   user-select: none;
   pointer-events: none;
-  transform-origin: center center;
+}
+
+.legendMarker {
+  position: absolute;
+  transform: translate(-50%, -50%);
+  width: 26px;
+  height: 26px;
+  border-radius: 50%;
+  background: #1e3a5f;
+  border: 2px solid #f5c542;
+  color: #fff;
+  font-size: 12px;
+  font-weight: 800;
+  display: grid;
+  place-items: center;
+  pointer-events: none;
+  z-index: 2;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.35);
 }
 
 .handle {