Various UX improvements and bug fixes

- Fix mustChangePassword session flag for users with pw=NULL
- Add PrF (Private Führung) as new ArtFuehrung type
- Split datetime-local into separate date + TimePicker5 (5-min steps, auto-repeat)
- Responsive Beginn/Ende layout: stacked on mobile, inline on desktop
- Sort BEOs alphabetically by Kürzel in selector
- Title shows active kuppel; hide user display in header
- Selected BEOs show Kürzel only (name stays in dropdown)
- Session timeout reduced to 1 hour
- Add CLAUDE.md

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

lib/session.ts

@@ -2,7 +2,7 @@ import { cookies } from 'next/headers';
 import { SignJWT, jwtVerify } from 'jose';
 
 const SESSION_COOKIE_NAME = 'logbuch_session';
-const SESSION_DURATION = 7 * 24 * 60 * 60 * 1000;
+const SESSION_DURATION = 60 * 60 * 1000;
 
 const secretKey = process.env.AUTH_SECRET || 'logbuch-secret-change-in-production';
 const key = new TextEncoder().encode(secretKey);