Fry3DX 0.4: an easy 3D modeller

Shapes with live settings, shape editing, knife and hole tools, drawing
shapes onto other objects, combining objects (add / subtract / overlap),
copies, thickness, painting with stickers and layers, a Layout tab, a
Print tab with checks, packed .fry files with autosave, export to GLB,
glTF, FBX, OBJ, 3MF, STL and PLY, folders in Layers, its own crash
screen, and a website for GitHub Pages in docs/.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NMSrd5oe1GpUD7E6d825KP

engine/core/time.h

@@ -0,0 +1,13 @@
+#pragma once
+#include <chrono>
+
+namespace keel {
+
+// Seconds since program start, monotonic.
+inline double now() {
+    using clock = std::chrono::steady_clock;
+    static const clock::time_point start = clock::now();
+    return std::chrono::duration<double>(clock::now() - start).count();
+}
+
+} // namespace keel