Add admin cockpit and API for managing locations

[achildrenmile]

Background

Locations are currently added and managed manually (see current approach in the repository README and codebase).
This does not scale well and is error-prone.

Description

Introduce a simple admin cockpit to manage location data securely.
Location data shall be stored in a lightweight database and served via an API endpoint to the frontend.

Scope

Admin Cockpit

• Simple web-based admin interface
• Create / update / delete locations
• Authentication required (security-first approach)
• Minimal but robust (no overengineering)

Security

• Secure authentication for admin access
• Follow best practices (no hardcoded secrets, least privilege)
• API endpoints protected as needed

API

• Provide a REST-style API endpoint to retrieve locations
• API used by frontend to display stations/locations
• Clear data contract (JSON)

Data Storage

• Use a lightweight persistence solution
  • e.g. SQLite
  • or another simple embedded / file-based DB
• Easy to back up and migrate
• Suitable for Dockerized deployments

Acceptance Criteria

• Locations are no longer hardcoded
• Locations can be managed via admin UI
• Location data is persisted
• API endpoint reliably serves location data
• Security considerations are documented

Notes

Focus on simplicity, security, and maintainability.
The solution should work well in a Docker-based setup.