feat: add OpenCV loader, Otsu threshold and margin-aware mask tracing

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

vite.config.ts

@@ -11,5 +11,7 @@ export default defineConfig({
     include: ['tests/**/*.test.ts'],
     testTimeout: 30000,
     hookTimeout: 60000,
+    // OpenCV's CJS export is a thenable; copying it onto the namespace makes `import()` never settle.
+    deps: { interopDefault: false },
   },
 });