Slice 1 follow-up: component-render interaction tests (CR-1/CR-2)

- vite: add @testing-library/svelte's svelteTesting() plugin so component
  render()/mount() resolves Svelte's browser build under vitest/jsdom
- dep: @testing-library/user-event for realistic interaction tests
- app: 7 component-render tests driving App.svelte through a fake socket
  (catalog render, subscribe-on-click, unsub/sub ordering, aria-current,
  error banner, action invoke)

Verified green: svelte-check 0/0, vitest 91 passed, biome clean, vite build ok.

1 files changed, 5 insertions, 6 deletions

diff --git a/vite.config.ts b/vite.config.ts
index fab62a0..5ff83cd 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,10 +1,14 @@
 import { svelte } from "@sveltejs/vite-plugin-svelte";
+import { svelteTesting } from "@testing-library/svelte/vite";
 import { defineConfig } from "vitest/config";
 
 // Dev server on the reserved FRONTEND_PORT (24204). Vitest config lives here too
 // (jsdom + globals) so component tests run without extra config.
 export default defineConfig({
-	plugins: [svelte()],
+	// svelteTesting() forces Svelte's `browser` resolve condition under vitest so
+	// component render()/mount() works in jsdom (a plain test.resolve.conditions
+	// does not propagate to Vite's SSR resolution — sveltejs/svelte#11394).
+	plugins: [svelte(), svelteTesting()],
 	// Bind all interfaces + accept any Host header so the dev server is reachable over a LAN /
 	// Tailscale. Safe for LOCAL-NETWORK-ONLY use (NOT internet-exposed): `allowedHosts: true`
 	// disables Vite's DNS-rebinding host check. (The WS URL still runs in the browser — set
@@ -14,10 +18,5 @@ export default defineConfig({
 		environment: "jsdom",
 		globals: true,
 		setupFiles: ["./vitest-setup.ts"],
-		// Svelte 5's exports map resolves `svelte` → server build under the default
-		// condition; force the browser build so component tests can mount().
-		resolve: {
-			conditions: ["browser"],
-		},
 	},
 });