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/routes/recover/+page.svelte

@@ -25,7 +25,7 @@
 				user_id: string;
 			}>('/recover', { display_name: displayName.trim(), pin: pin.trim() });
 
-			setAuth(res.jwt, pin.trim(), res.user_id);
+			setAuth(res.jwt, pin.trim(), res.user_id, displayName.trim());
 			goto('/feed');
 		} catch (e) {
 			if (e instanceof ApiError) {