Add mocked unit tests for REST API route handlers

Tests the full handler flow with mocked DB: auth guard (401), Zod
validation (400), successful responses, and 404s for missing resources.
Also adds ~ alias resolution to Journal vitest config.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/journal/vitest.config.ts

@@ -1 +1,11 @@
-export { default } from "../../vitest.shared.ts";
+import { defineConfig, mergeConfig } from "vitest/config";
+import shared from "../../vitest.shared.ts";
+import { resolve } from "node:path";
+
+export default mergeConfig(shared, defineConfig({
+  resolve: {
+    alias: {
+      "~": resolve(import.meta.dirname, "app"),
+    },
+  },
+}));