feat: implement local authentication mode and update related components

frontend/src/auth/localAuth.ts

@@ -0,0 +1,43 @@
+"use client";
+
+let localToken: string | null = null;
+const STORAGE_KEY = "mc_local_auth_token";
+
+export function isLocalAuthMode(): boolean {
+  return process.env.NEXT_PUBLIC_AUTH_MODE === "local";
+}
+
+export function setLocalAuthToken(token: string): void {
+  localToken = token;
+  if (typeof window === "undefined") return;
+  try {
+    window.sessionStorage.setItem(STORAGE_KEY, token);
+  } catch {
+    // Ignore storage failures (private mode / policy).
+  }
+}
+
+export function getLocalAuthToken(): string | null {
+  if (localToken) return localToken;
+  if (typeof window === "undefined") return null;
+  try {
+    const stored = window.sessionStorage.getItem(STORAGE_KEY);
+    if (stored) {
+      localToken = stored;
+      return stored;
+    }
+  } catch {
+    // Ignore storage failures (private mode / policy).
+  }
+  return null;
+}
+
+export function clearLocalAuthToken(): void {
+  localToken = null;
+  if (typeof window === "undefined") return;
+  try {
+    window.sessionStorage.removeItem(STORAGE_KEY);
+  } catch {
+    // Ignore storage failures (private mode / policy).
+  }
+}