fix(test): disable solid HMR in tests to fix path error on Windows (@nadalaba) (monkeytypegame#7677)

### Description

Solid’s refresh runtime is injecting a virtual module that resolves to
an invalid `file:///@` URL causing tests to fail on Windows:

> TypeError: The argument 'filename' must be a file URL object, file URL
string, or absolute path string. Received 'file:///@solid-refresh'

HMR isn’t used in vitest's SSR test environment, so disabling it on all
platforms is safe.

Author: nadalaba

frontend/vitest.config.ts

@@ -6,7 +6,7 @@ import solidPlugin from "vite-plugin-solid";
 const plugins = [
   languageHashes({ skip: true }),
   envConfig({ isDevelopment: true, clientVersion: "TESTING", env: {} }),
-  solidPlugin(),
+  solidPlugin({ hot: false }),
 ];
 
 export const projects: UserWorkspaceConfig[] = [