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/api/client.ts

@@ -0,0 +1,32 @@
+export interface ApiError {
+  error: string;
+  status: number;
+}
+
+async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
+  const resp = await fetch(path, {
+    method,
+    credentials: "include", // send/receive the signed session cookie
+    headers: body !== undefined ? { "Content-Type": "application/json" } : undefined,
+    body: body !== undefined ? JSON.stringify(body) : undefined,
+  });
+
+  const text = await resp.text();
+  const data: unknown = text ? JSON.parse(text) : {};
+
+  if (!resp.ok) {
+    const message =
+      typeof data === "object" && data !== null && "error" in data
+        ? String((data as { error: unknown }).error)
+        : "Request failed.";
+    const err: ApiError = { error: message, status: resp.status };
+    throw err;
+  }
+
+  return data as T;
+}
+
+export const api = {
+  get: <T>(path: string) => request<T>("GET", path),
+  post: <T>(path: string, body?: unknown) => request<T>("POST", path, body),
+};