feat: implement My Account page

Add /account route showing display name (from localStorage), role badge,
session expiry decoded from JWT, and recovery PIN display with copy button.
Join and recover flows now persist display_name to localStorage via setAuth().
Feed header logout button replaced with person-icon link to /account;
logout is available from the account page.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/auth.ts

@@ -4,6 +4,7 @@ import { browser } from '$app/environment';
 const TOKEN_KEY = 'eventsnap_jwt';
 const PIN_KEY = 'eventsnap_pin';
 const USER_ID_KEY = 'eventsnap_user_id';
+const DISPLAY_NAME_KEY = 'eventsnap_display_name';
 
 export const isAuthenticated = writable(false);
 
@@ -22,11 +23,28 @@ export function getUserId(): string | null {
 	return localStorage.getItem(USER_ID_KEY);
 }
 
-export function setAuth(jwt: string, pin: string | null, userId: string): void {
+export function getDisplayName(): string | null {
+	if (!browser) return null;
+	return localStorage.getItem(DISPLAY_NAME_KEY);
+}
+
+export function getExpiry(): Date | null {
+	const token = getToken();
+	if (!token) return null;
+	try {
+		const payload = JSON.parse(atob(token.split('.')[1]));
+		return payload.exp ? new Date(payload.exp * 1000) : null;
+	} catch {
+		return null;
+	}
+}
+
+export function setAuth(jwt: string, pin: string | null, userId: string, displayName?: string): void {
 	if (!browser) return;
 	localStorage.setItem(TOKEN_KEY, jwt);
 	if (pin) localStorage.setItem(PIN_KEY, pin);
 	localStorage.setItem(USER_ID_KEY, userId);
+	if (displayName) localStorage.setItem(DISPLAY_NAME_KEY, displayName);
 	isAuthenticated.set(true);
 }