test: add vitest-canvas-mock for local canvas support

Fixes UILayer tests failing locally due to the native canvas package
not being compiled. vitest-canvas-mock provides a jsdom-compatible
Canvas 2D API mock without requiring native build tools.

tests/setup.ts

@@ -1 +1,2 @@
 // Add global mocks or configuration here if needed
+import "vitest-canvas-mock";