Android Ski Resort Time-Tracker

I need a small, German-language Android app that lets the crew at our Skigebiet log their shifts and grooming work in a clean, structured way. We are only ten people, so a lightweight email-and-password login is enough; no social logins or open access.

Hauptseite – Arbeitszeit
• Each user starts and stops a timer or enters start/stop times manually.
• I must be able to pull weekly and monthly summaries per user and for the whole team, then export those reports as CSV straight from the device.

Zweite Seite – Präparierte Loipen
After clocking out, the user chooses the routes they just prepared. The fixed list must appear exactly like this:
– Loipe Säätliboden (Rüti GL)
– Nidfurn – Leuggelbach
– Rundkurs Leuggelbach
– Schwanden - Nidfurn – Schwanden
– Luchsingen - Hätzingen (Skistübli)
– Hätzingen – Linthal

Dritte Seite – Spesenbelege
Option to snap a photo or pick an image/PDF of a receipt incurred during the shift and upload it so I can download everything later.

Weitere Anforderungen
• Clear German UI texts; no mixed languages.
• Works on current Android versions, offline capable for bad mountain reception, and syncs when back online.
• Simple admin view (can be in-app or browser) to create/edit the ten user accounts, reset passwords, and download the CSV reports and uploaded receipts.
• Source code and installable APK are the final deliverables; please include a short read-me so I can rebuild if needed.

If you can build this with a familiar stack such as Kotlin + Room/WorkManager or Flutter + Firebase, great—just keep the setup straightforward and documented.