fix(HAI-018): complete Step 1 — fix server-side error handling in GET /tasks/:id

- Route now returns 404 only for ENOENT, 500 for transient errors
- store.getTask() retries once after 50ms on non-ENOENT failures
- Added route tests for success, 404, and 500 cases
- Updated vitest config to include src/**/*.test.* files

packages/dashboard/vitest.config.ts

@@ -11,6 +11,6 @@ export default defineConfig({
   },
   test: {
     environment: "jsdom",
-    include: ["app/**/*.test.{ts,tsx}"],
+    include: ["app/**/*.test.{ts,tsx}", "src/**/*.test.{ts,tsx}"],
   },
 });