Add Vitest, jsdom and importer tests

Set up testing with Vitest and jsdom and add unit tests for importers (jellyfin, playnite, stashapp, xbvr). Add typedoc configuration and update vite.config.ts and importer source files to support the tests. Ignore generated docs by adding /docs to .gitignore and add test-related devDependencies (vitest, @vitest/ui, jsdom, typedoc) in package.json.

vite.config.ts

@@ -17,8 +17,13 @@ export default defineConfig(({mode}) => {
     },
     server: {
       // HMR is disabled in AI Studio via DISABLE_HMR env var.
-      // Do not modify—file watching is disabled to prevent flickering during agent edits.
+      // Do not modify—file watching is disabled to prevent flickering during agent edits.
       hmr: process.env.DISABLE_HMR !== 'true',
     },
+    test: {
+      globals: true,
+      environment: 'jsdom',
+      setupFiles: [],
+    },
   };
 });