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>

app/login/actions.ts

@@ -21,15 +21,17 @@ export async function login(
     return { error: 'Ungültiges Kürzel oder Passwort.' };
   }
 
+  const mustChange = result.beo.MustChangePassword === 1 || !result.beo.pw;
+
   await createSession({
     kuerzel: result.beo.kürzel ?? kuerzel,
     beoId: result.beo.id,
     beoName: getBeoDisplayName(result.beo),
-    mustChangePassword: result.beo.MustChangePassword === 1,
+    mustChangePassword: mustChange,
     isAuthenticated: true,
   });
 
-  if (result.beo.MustChangePassword === 1 || !result.beo.pw) {
+  if (mustChange) {
     redirect('/change-password');
   }