M0: Vue 3 + TypeScript frontend — auth views + authed board shell

- Vite + Vue 3.5 + Pinia + vue-router + Tailwind (brand accent #F5C518),
  dark-mode aware, deterministic package-lock.json for `npm ci`.
- Session store (fetchMe/login/register/logout) over a credentials:'include'
  fetch client; router guards (requiresAuth / guestOnly) with lazy /me resolve.
- BaseButton + BaseInput primitives (focus rings, loading, error states).
- LoginView, RegisterView, and an authed BoardView shell with an empty state
  for the M1 masonry board — all at v1 polish (rule 24).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/router/index.ts

@@ -0,0 +1,43 @@
+import { createRouter, createWebHistory } from "vue-router";
+import { useSessionStore } from "../stores/session";
+
+const router = createRouter({
+  history: createWebHistory(),
+  routes: [
+    {
+      path: "/",
+      name: "board",
+      component: () => import("../views/BoardView.vue"),
+      meta: { requiresAuth: true },
+    },
+    {
+      path: "/login",
+      name: "login",
+      component: () => import("../views/LoginView.vue"),
+      meta: { guestOnly: true },
+    },
+    {
+      path: "/register",
+      name: "register",
+      component: () => import("../views/RegisterView.vue"),
+      meta: { guestOnly: true },
+    },
+  ],
+});
+
+router.beforeEach(async (to) => {
+  const session = useSessionStore();
+  // Resolve the current user once, lazily, before the first guarded navigation.
+  if (!session.loaded) {
+    await session.fetchMe();
+  }
+  if (to.meta.requiresAuth && !session.user) {
+    return { name: "login", query: to.fullPath !== "/" ? { redirect: to.fullPath } : undefined };
+  }
+  if (to.meta.guestOnly && session.user) {
+    return { name: "board" };
+  }
+  return true;
+});
+
+export default router;